Calibration:

To determine, check, or rectify the graduations of (any instrument giving quantitative measurements). ¹  Calibration is the comparison between the output of a scale or balance against a standard value.  Calibration requires a standard weight and the balance to be set in the "calibration mode." 

Calibration technically means to determine the difference between the balance/scale readout and the actual weight on the weighing platform to determine accuracy.  Adjustment means to bring a balance/scale into the state of accuracy required for its use.  Therefore, 'calibration," actually means "adjustment."

Some instruments contain internal calibration weights that are quite accurate, and can be used by the operator routinely, but we recommend external calibration.  The readability of the scale will determine which class calibration mass (Class 1, Class 2, ASTM 6, Class F, etc) will be appropriate for calibrating your balance.  Check your operator’s guide since most balances must be calibrated with a specific mass value.

Example: the Ohaus CS200 requires a 200 gram ASTM Class 6 mass.  You can not calibrate the CS200 if you have a 100 gram mass.  It must be a 200 gram mass.  The scale is programmed and the software within the scale is configured only to accept a 200 gram calibration value to store the calibration data within the EPROM on the scale’s motherboard.

Calibration Certificate:

There is no certificate of calibration included with any balance we sell since this can only occur at the place of installation.  A calibration certificate can only be attained at the place of installation for a balance.  One can't calibrate a balance here in Massachusetts and ship it to another destination with the calibration certificate that would be valid.

The reason for this included:

• Any location in the world is positioned differently from "magnetic north", thus effecting the acceleration of gravity, which effect the force a cal mass exerts on the balance's weighing sensor.
• Barometric Pressure makes a difference and if the balance is calibrated in the hills of the rocky mountains and you're at sea level say in the California Bay Area your elevation is different effecting the barometric pressure.
  

You can purchase optional calibration weights for most balances, but the question then becomes do you needs weights with a "certificate of accuracy", "calibration report" or "mass value certificate".  Read more about calibrations weights and the huge selection we offer at http://calibration.balances.com/.

Basically local scale companies are in business just for this reason of calibrating and providing the documentation requirements.  You might want to call a local scale company to see what they charge.  Regardless, calibration certificates is something neither Precision Weighing Balances nor the scale manufacturer can offer unless we come on site to install the balance.  Calibration is an additional service and this is always best done exactly at where the balance is in operation.

Another option to attain a certificate of calibration is to do it yourself with a certified calibration mass which we sell.  You can basically copy the calibration instructions in the manual and create a QAD (Quality Assurance Directive), QAP (Quality Assurance Procedure) or SOP.  You can also create your own calibration procedure from scratch like this one here. 

People sometimes call us saying a competitor or catalog company offered to ship their balance with a calibration certificate if they purchase the balance from them.  Companies offering balance(s) with a calibration certificate are providing false documents unless the calibration is performed on site.  Sure, companies can sell a oscilloscope or power supply with a certificate of calibration when the power supply is calibrated halfway across the country since a power supply isn't effected by the different longitude and latitude of magnetic north like a balance.

Looking for calibration weights?  Check out our huge selection

Calibration error

Capacity

The actual or potential ability to perform, yield or withstand. ¹  The largest weight the balance is capable of weighing.

Capacitance Loadcell

The fundamental design of a capacitance loadcell is that of the electrical capacitor.  The loadcell contains two closely spaced, parallel, electrically-isolated metallic surface, one of which is essentially a diaphragm capable of slight flexing when pressure is applied.  When pressure is applied to the capacitance loadcell a minute change occurs in distance between the plates.  The varying gap between the plates creates in effect a variable capacitor.  The resulting capacitance is detected send to a linear comparator and amplifier which is then processed by a microprocessor and displayed on the LCD.  Dendritics, and many of the Tanita Pocket and Foods Scales use a capacitance loadcell.

Cornerload

Cornerload error

Divisions

The amount of increments a scale offers.  The amount of divisions can be determined by taking the scale's capacity divided by the scales readability (the smallest number a scale can display.  Example the Ohaus SC4010 features 4,000 divisions.  The capacity is 400 grams and the scale's readability or another way to say it is the numbers on the display increase in 0.1 gram intervals.  Therefore 400 / 0.1 = 4,000 divisions.  Another example would be the Ohaus SC2020 features 20,000 divisions.  The capacity for the SC2020 is 200 grams and the scale's readability is 0.01 gram.  Therefore 200 / 0.01 = 20,000 divisions.  It is the divisions which determines the cost of a scale - not the capacity or readability, but instead the combination of both the capacity and readability to determine the amount of divisions.  The more divisions the better the quality of the weighing sensor and larger the A/D converter needed to resolve the analog output from the weigh sensor to a binary number for the digital display.

Flexible Bearings - Precision components in the measuring cell (force motor) which allow the force coil to move without friction.

Force Motor (a.k.a Electromagnetic Force Compensation) - See a detailed explanation with detailed drawing here. Also call" measuring cell."

© Crown Copyright 2004. Reproduced by permission of the Controller of HMSO

Hysteresis - Property of load cells, and other weighing systems dependant on elastic materials, such as spring balances, resulting in a different indication at the same load, depending upon the direction of approach to that load, i.e. whether it is approached by increasing the load or decreasing the load.  It is most pronounced at the mid-point of the weighing range. The lag in response exhibited by a body in reacting to changes in forces, esp. magnetic forces, affecting it.

The diagram (Fig 1) is from the UK's National Physical Laboratory and illustrates the concept quite well.

Hysteresis Error - Refers to the condition of repeatedly weighing the same object, but obtaining different readings on the numeric readout.

Instability - the tendency to behave in an unpredictable, changeable, or erratic manner. ¹  Refers to a displayed number which continues to vary randomly or sporadically, rather than progressively. See "drift."

Installation - Learn about selecting the best location of your balance for optimal performance.

Internal resolution - the smallest increment of the A/D converter.  It is used by the hardware and software designers.  For a scale using a strain gauge design, the ratio between internal and display resolution is about 4:1.  For a balances (force motor or SHS design), the ratio can be 10:1.  It is possible to use 1:1 ratio, but you will see a lot of unstable readings by changing of 1 increment.  Having stable display is the main reason of the ratio.  There are other concerns, such as measurement speed and temperature compensations.

A&D offers more flexibility to the counting scale user.  At 1/30,000 setup (models HC and HD, the FC is 1/50,000), you can not count very small piece materials, but your counting results will be more stable on the LCD display.  It takes a drift of 4 internal counts (at 1/120,000 setup - FC is 1/500,000) to show one count change on the display.  Internally, A&D HC and HD counting scales always uses 1/120,000 mode(FC is 1/500,000).  This is a benefit/flexibility to customers.  In the measurement industry, we care of the most is the "accuracy".

IP Ratings (Ingress Protection) - The IP rating system provides a means of classifying the degrees of protection from solid objects and liquids afforded by electrical equipment and enclosures.  The system is recognized in most European countries and is set out in a number of British and European standards. These include: Classification of Degrees of Protection Provided by Enclosures, BS (British Standards) 5490:1977; IEC (International Electrotechnical Commission) 529:1976.

Specifications for Degrees of Protection of Enclosures of Switchgear and Control Gear for voltages up to and including 1000 VAC and 1200 VDC, BS 5420:1977; and IEC 144:1963.

First number Protection against solid objects
0 - no protection
1 - protected against solid objects up to 50 mm (e.g. accidental touch by hands)
5 - protected against dust-limited to ingress (no harmful deposits)
6 - totally protected against dust

Second number Protection against liquids
0 - no protection
1 - protected against vertically falling drops of water (e.g. condensation)
2 - protected against direct sprays of water up to 15° from the vertical
4 - protected against water sprayed from all directions—limited ingress permitted
6 - protected against strong jets of water—limited ingress permitted (e.g. for use on ship decks)
7 - protected against the effects of immersion between 15 cm and 1 m
8 - protected against the effects of extended periods of immersion under pressure

IP-43 Rating - The first digit designation "4" means protection against "solid objects equal or greater than 1mm (0.04") in diameter".  The second digit "3" means protection against "sprayed water" ; "Spray water falling perpendicularly at an angle of up to 60-deg may not have any damaging effects".

IP-54 Rating - The "5" means "Dust Protected.  Ingress of dust is not totally prevented, but dust does not enter in sufficient quantity to interfere with satisfactory operation of the equipment.  The "4" means "Protected against splashing water.  Water splashed against the enclosure from any direction shall have no harmful effect."

IP-66 Rating - A strong water jet directed at the scale from any direction must not have any harmful effects.  A jet nozzle with an inside diameter of 0.49 inches splashes a volume flow of approximately 26.4 gallons per minute, from a distance of approximately 8.2 - 9.8 Feet from all sides onto the scale.  The test time is 3 minutes.

IP-67 Rating - Temporary Submersion.  The device is placed in water at a depth of 3.28 feet for 30 minutes

IP-68 Rating - Long Term Submersion

IP-69K Rating - A strong water jet directed at the sensor from 4 directions must not have any harmful effects.  A jet nozzle at 0°, 30°, 60° and 90° to the scale on a rotating table at 176° + 8°F, 4-6 inches away at 1250-1500psi.  The test time is 2 minutes.

Light Emitting Diode (LED) - A type of solid-state numeric readout device.  Often characterized by red or orange-red numbers.

Liquid Crystal Display (LCD) - A numeric readout device, often characterized by black numerals on a silver background.

Mass tolerances - weight classifications & applications:

ASTM Class 1: Can be used as a reference standard in calibrating other weights and is appropriate for calibrating high precision analytical balances with a readability as low as 0.1mg to 0.01mg.

ASTM Class 2: Appropriate for calibrating high-precision top loading balances with a readability as low as 0.01g to 0.001g.

ASTM Class 3: Appropriate for calibrating balances with moderate precision, with a readability as low as 0.1g to 0.01g.

ASTM Class 4 -For calibration of semi-analytical balances and for student use.

NIST Class F - primarily used to test commercial weighing devices by state and local weights and measures officials, device installers and service technicians.  Class F weights may be used to test most accuracy class III scales, all scales of class III L or IIII, and scales not marked with a class designation. Calibrated according to NIST Handbook 105-1

OIML Class E1 - Used as primary reference standards for calibrating other reference standards and weights.

OIML Class E2 - Can be used as a reference standard in calibrating other weights and is appropriate for calibrating high precision analytical balances with a readability as low as 0.1mg to 0.01mg.

OIML Class F1 - Appropriate for calibrating high-precision toploading balances with a readability as low as 0.01g to 0.001g.

OIML Class F2 - For calibration of semi-analytical balances and for student use.

OIML Class M1, M2, M3 - Economical Weights for general laboratory, industrial, commercial, technical and educational use.  Typically fabricated from cast iron or brass. Class M2 commonly used for student brass weights.

Measuring Cell - (Also known as a force motor.) is the part of the instrument which "senses" weight, and converts it to an electrical signal.  Similar to "mechanical system" or "force motor."

Min Weight - typically used in the specifications of counting scales.  The small piece weight required in a counting mode.  At the beginning of any counting process, the scale's software needs to teach the scale what is the unit piece weight.  The scale uses the information to count the unknown weight.

A&D offers more flexibility to the counting scale user.  At 1/30,000 setup (models HC and HD, the FC is 1/50,000), you can not count very small piece materials, but your counting results will be more stable on the LCD display.  It takes a drift of 4 internal counts (at 1/120,000 setup - FC is 1/500,000) to show one count change on the display.  Internally, A&D HC and HD counting scales always uses 1/120,000 mode(FC is 1/500,000).  This is a benefit/flexibility to customers.  In the measurement industry, we care of the most is the "accuracy".

Moisture Balance heating elements:

• Ceramic - is a great heating material however it take slightly longer to warm up and longer to cool down. So in general it will  take a little bit longer during analysis (we're talking seconds to minutes longer) but more importantly it takes longer for the heating element to cool down and get back to starting temp (baseline). However ceramic offer the most consistent heating of all samples type and slowly ramping temp can be ideal some case where the most precision and repeatability is needed. It also great for difficult sample types like once which vaporize quicly or hydroscopic. See the Sartorius MA150C
  
  
• Halogen - is super speedy which is great for the person who wants quick results and has a less stringent SOP's about repeatability or just need a tolerance check to meet limits. However, Halogen does have a reputation for  scorching or burning samples which can cause erroneous errors in result and can tend to over shoot endpoint.See the Sartorius MA100H
  
  
• Quartz - is the middle guy it speeder than ceramic but not over zealous like halogen.It will still give consistent heating while offering faster results.
  
  
• Summary - With that said, all three can be ideal and have benefits with certain sample types....this is why the first question we ask the customer in moisture world
  1) What are you cooking (aka what is the sample type)?
  2) What %M or %S is typically for your samples result?
  
  

NTEP / Type Approved / Legal for Trade - The National Type Evaluation Program (NTEP) evaluates commercial measuring devices and issues Certificates of Conformance to those devices that meet national and/or international standards.  In this way, consumers are protected and can be confident that they are charged fairly for goods or services rendered.

Type evaluation is the process whereby weighing and measuring devices are examined by government officials to determine if the design and performance comply with the Weights and Measures requirements of the country in which the manufacturer wishes to market the device for commercial applications.

The purpose of type evaluation is to examine the design, features, operating characteristics, and performance of weighing and measuring devices for compliance with Weights and Measures requirements.  Such tests are performed on sample devices under laboratory conditions.  Read more about NTEP approved / legal for trade scales here.  To see all the Legal for Trade, Class III scales we offer click here.

Precision - The extent to which a given set of measurements of the same sample agree with their mean. ¹  Amount of agreement between repeated measurements of the same quantity.  Also know as repeatability.  A scale can be extremely precise, but not necessarily be accurate.  Example, two balances were evaluated for precision.  Both balances: Balance "A" and Balance "B" offers 200g x 0.001g.  A 100.000 gram ASTM Class 1 test mass was place on each balance 70 times.

Readability - Smallest division at which the balance’s LCD increments. 

Examples:Ohaus CS2000 features a 2000 gram weighing capacity and increment in 1 gram increments (2000g x 1g.)  Therefore, the readability is 1 gram.  The LCD will increment 1 g, 2 g, 3 g, 4 g, .... 1999 g, 2000 g.  You will never see 0.1 g or 0.5 g with the CS2000.  The scale manufacturer also defines the CS2000 scale with an accuracy of +/- 3 grams, but a readability of 1 gram.  Therefore the scale increments in 1 gram intervals but it is on accurate to +/- 3 grams.

Tanita KD200-110 increments in 1 gram intervals.  This means when weighing item(s) on the weighing platform from 0 to 1000 grams the LCD will increment from 0 to 1 g, 2 g, 3 g, ... 999 g, 1000 g.  Again you will never see the LCD show 0.1g or 0.5 grams.  The display will ALWAYS BE IN WHOLE GRAM increments.  Therefore, if you need 0.1 accuracy you need to look at A&D EK1200G (1200g x 0.1g) since they don't make a scale that is 1000g x 0.1g..

Tanita 1140 is a dual range scale.  This means when weighing item(s) on the weighing platform from 0 to 500 grams the LCD will increment from 0 to 1 g, 2 g, 3 g, ... 499 g, 500 g.  Again you will never see the LCD show 0.1g or 0.5 grams.  The display will ALWAYS BE IN WHOLE GRAM increments.  When the weight on the platform exceed 500 grams (501 - 1000g) the LCD will increment in 2 gram intervals automatically.  You have no control of this since the manufacturer has programmed the scale to operate in 2 gram intervals when anything is placed on the platform over 500 gram.  Therefore, the display will show 502 g, 504 g, 506, up to 996 g, 998 g, 1000 grams.

The Tanita 1479(grams only version), Tanita 1471(grams & ounce version), Tanita 1477 (grams & pennyweight), Tangent KP102(gram only) and many other pocket scales operate with a dual range except they read at 0.2 grams.  This means when weighing item(s) on the weighing platform from 0 to 50 grams the LCD will increment from 0.0 to 0.1 g, 0.2 g, 0.3 g, ... 49.9 g, 50.0 g.  Again you will never see the LCD show anything less than 0.1g when purchasing a pocket scale.  When the weight on the platform exceeds 50.0 grams (50.1 - 100.0g) the LCD will increment in 0.2 gram intervals automatically.  You have no control of this since the manufacturer has programmed the scale to operate in 0.2 gram intervals when anything is placed on the platform over 50.0 gram.  Therefore, the display will show 50.2 g, 50.4 g, 50.6, up to 99.6 g, 99.8 g, 100.0 grams.

Reproducible - Refers to the ability of an instrument to return the same numeric result with repeated application of the same weight.  See " hysteresis."

Resolution - The smallest increment of weight which the numeric display can indicate.  Also referred to as 'display resolution".

Here are two explanations for sensitivity to drift:

The sensitivity drift is how a change in temperature can affect the performance of the balance.  Basically it states what the user can expect to see from the balance when the temperature changes. This phenomenon is more relevant on micro balances which offer resolutions up to 0.001mg.  The change in temperature is measured by a thermistor in the weighing cell which sends the value to the A/D converter module.

As an example, the A&D GF-600 which has a specification for sensitivity to drift at ± 2ppm /°C.  If there were 30g on the balance & there was an increase in the temperature of 10°C the weight change would be 0.0006g [weight in grams x sensitivity to drift x temp change in °C so 30 x (0.000002 x 10)].  With the resolution of the balance being at 1mg (0.001g) you would most likely only see a change of 1 division.  Obviously the balance would show more of this effect as the change in temperature increases.

Here is a second explanations for sensitivity to drift:

All electronic balances are susceptible to a weight reading drifting due to environmental temperature changes.  The measure of this drift is called sensitivity drift.

Sensitivity drift relates this temperature affect at a given weight.  For example, for a 2.1g x 0.1ug Sartorius SE2 micro balance with a sensitivity drift spec of ± 1ppm per degree C and a 1 gram weight on the pan, the balance will drift 1 ug (0.000001g) for every degree of change in temperature.  So if your micro balance is in a separate room with no temperature control and 2 or 3 person walk into the room resulting in a temperature increases by 2°C sensitivity of drift becomes an issue.  If the test was to determine particles captured on a 2 gram filter where the filter is weighed, then the filter is placed into the exhaust air stream of a piece of equipment being measure for emissions and the filter is now weighed again the delta might be 10ug.  The problem is if the temperature was raised by 2°C then 4 ug [weight in grams x sensitivity to drift x temp change in °C so 2 x (0.000001 x 2)] is the result of sensitivity to drift and 6ug is the weight of particles captured in the filter.  Here sensitivity to drift dramatically effects the weighing results.

Every time you recalibrate a balance, this drift starts over at zero.  This is why Sartorius puts their ISO Cal technology into a balance and why some metrology handbooks recommend recalibrating a balance at different times of the day.

As you can tell, for anything other than micro balances, it really does not matter that much as the drift spec is lower than the repeatability and linearity specs of most of the models offered.

Many manufacturer's do not have a sensitivity drift spec for any of their models including the 0.1mg models since sensitivity to drift only effects balances with readability to 0.01mg, 1ug or 0.1ug.

If a customer is really concerned about sensitivity drift, the best thing for them to do is recalibate the balance on a continual basis.

Span Calibration:

Span calibration utilizes two calibration points, one at zero and a choice of either half capacity or full capacity.

Strain Gauge Transducer

Commonly called a loadcell.  Consists of an aluminum beam with 4 strain gauges bonded at the hinge areas.  The strain gauge is packaged as a film and when the strain gauge is bent the resistance value changes, similar to a potentiometer.  The 4 gauges are wired to form a wheatstone bridge.  When a load is placed on the beam, it bends at the flexures.  The bending changes the resistance value of the strain gauges (normally 350 ohms at rest) and the resulting output from the wheatstone bridge is proportional to the load.

With the basic understanding of electronics including "Ohm’s Law" in which Voltage = Current x Resistance and the understanding that current is the same in a series circuit you will be able to understand the functionality of a load cell.

Two points of the wheatstone bridge are connected to an exciter voltage (from the battery or AC adapter) and an output analog voltage feed to a A/D Converter.  The output voltage being fed in the A/D varies in proportion to the load applied to the platform of the scale.  This occurs since the weighing platform of a scale is connected to the end of the load cell via a post.  The applied force is transferred from the platform, through the post and onto the aluminum beam.  Since the aluminum beam is milled out in the shape of a dog bone, the force applied results in a deformation of the beam.  When the beam bends the strain gauges bend resulting in their resistance value to change.  Since the current is the same in a series current and the resistance changes as the strain gauges bends, the voltage changes in proportion to the load applied to the platform.

The analog voltage is converted by the A/D into a digital signal which is processed by a microprocessor and the microprocessor outputs the appropriate control signals to illuminate the corresponding segments of the LCD to display the correct numerical number for a user to read from the LCD.  In between the steps there are some filters, but basically there really isn’t much to a scale.

The problem with scales incorporating a load cell is that an excessive load can permanently bend the load cell.  If the aluminum beam is permanently bent the scale will not work.  This is NOT covered under the scale manufacturer’s warranty.  In most situations the cost of replacing the load cell cost almost as much a replacing the scale, because of the ‘deep discount prices" we offer.  For example Ohaus charges approximately $90.00 to replace the load cell on the SP401 while we sell a brand new Ohaus SP401 for $142.00.

Therefore, great care needs to be taken when using a scale with a load cell.  The person needs to have an idea how much an object weighs prior to placing it on the platform.  Otherwise, you can destroy the scale.

The best way I describe this is if you go out and buy a brand new bicycle.  Everything works great and you cruise down the street and hit a small pot hole.  The bicycle’s rim doesn’t get bent yet, but you have stressed the metal of the rim.  Now you decide to jump a few curbs and the rim is still okay.  You feel stupid today, and decide to hit that pothole again.  Now the rim is bent.  You can’t go back to the bicycle dealer and say the bike is junk since the rim in bent.  The rim got bent due to abuse and this is not covered under the manufacturer’s warranty.  Well, the same works with scale that incorporates a loadcell.  Many people don’t have an idea what something weighs prior to putting the object on the platform but you really need to get acquainted with what objects weigh prior to placing the object on the platform.  The manufacturers have taken precautions by installing a down stop which restricts the downward movement of the loadcell but prudence still must be followed.

Switches

Membrane Switches or displays that use tactile membrane switch panel are relible but they don't work in a vacuum.  These use a foil contact point.

Micro Switches are switches that make contact when the micro switch is pushed.  Typically micro switches cost more and are in the more expensive balances like the Acculab ALC Series or Sartorius Extend Series.

Act of removing a known weight of an object, usually the weighing container, to zero a scale.  Taring allows you to display the weight of the material on the scale's LCD with the weight of the material only and not the material and container.  Most balances allow taring to 100% of the weighing capacity.

Tare by subtraction means that you can keep on using the tare button providing the total mass on the platform does not exceed the weighing capacity of the scale.  Therefore, if you had the Tanita KD200-510 (5000g x 5g) and you put a pot on the scale that weighed 1000 grams and pressed the tare button the scale would display 0.0 and you would now have 4000 grams weighing capacity left (5000 - 1000 = 4000 g.)  Then you put 500 gram olive oil in the pot and press the tare button the scale would display 0.0 and you would now have 3500 grams weighing capacity left (5000 - 1000 - 500 = 3500 g.) etc, etc.

Temperature Range

Digital scales are electronic devices.  All electronic devices contain electronic components that have temperature coefficient.  An example of this would be a resistor.  If you measure a resistor with an Ohm meter and it measures 10 ohms at 0 degrees F and you then put that resistor in an environment chamber and bring the temperature up to 100 degrees F the resistance's value now could be 10.2 ohms.  Since the resistance value has increased this is an example of a discrete component(a resistor) having a "positive temperature coefficient".  Well, enough with electronics 101.

How does operating a scale above the manufacturer's operational temperature effect you?  The temperature operational range is stated since the manufacturer has tested and confirmed that his scale will have an accuracy (scale manufacturers' use the word "LINEARITY") of +/- however many grams provided you operate the scale within the stated temperature.  If you go outside of this temperature the scale may be off by a division (in the case of the Ohaus SC6010 <600 g x 0.1g> a division is 0.1 gram so that means it maybe off by +/-0.2 grams instead of the stated +/- 0.1 gram).  Like all electronic devices it is not a good ideal to operate them all day at excessive temperatures.  Will they operate?, Yes.  Consider your computer, this also has a temperature operating range.  Can you run your computer in an environment that is a 100 degrees?, Yes.  Do you want to do this all the time?, No because it stress the components. 

General Product Features

Power Up Test: When the scale is turned on, all display segments will appear for approximately 3 seconds before resetting to zero.

Stable Reading Indication: During weighing, a segment of the display activated once a stable reading has been reached.

Overload: If the applied load exceeds the capacity of the scale, an "E"' will appear on the display and the load should be removed immediately. The scale will return to normal operation.  Excessive overloading the scale can destroy the load cell and this is not covered under warranty.

Negative Value: When a load is removed from the scale, any tared value will be displayed as a negative number. To return to normal operation, the tared value can be canceled by pressing the tare button.

Zero Function: Values can progressively be added to a sample. By pressing the tare key, the scale display returns to zero and an indication appears at the upper left corner of the display.

Auto Shut-Off: To extend battery life, the scale will automatically turn off after approximately two to five minutes(depending on scale manufacture) if no active weighing is occurring.

Off: Pressing this key turns the scale off.

Conversions
1 grain = 0.0648 grams
1 gram = 15.4324 grains
1 gram = 0.643 pennyweights
1 gram = 0.03215 troy ounces
1.55517 grams = 1 pennyweight
28.3495 grams = 1 avoirdupois ounce
31.10348 grams = 1 troy ounce
1 kilogram = 32.15076 troy ounces
1 pennyweight = 24 grains
1 pennyweight = 0.05 troy ounces
20 pennyweights = 480 grains
20 pennyweights = 1 troy ounce
14.583 troy ounces = 1 avoirdupois pound
1 troy ounce = 1.09714 avoirdupois ounce