Calibration &
Test Weights


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Weights:Table of Contents

 Calibration & Test Weights

1.   An Overview of the Main Types of Weights Available.

Cast Iron Grip Handle, Flat and Slotted Calibration Weights

   Cast Iron Individual Test Weights and Weight Sets
Economical and rugged, these cast iron weights are manufactured with uniform materials and sealed with a lead plug to NIST Class F or ASTM Class 7 tolerances. Used for testing as well as calibration services.

Gram Weight Sets and Fractional or Decimal Ounce Sets for Testing and Calibration Services

   Brass Individual Calibration Weights and Weight Sets
 Economically priced, these weights are sealed to ASTM Class 6 or OIML Class M1 and are a popular choice for schools, universities and home use. Used for testing as well as calibration services.

  Stainless Steel Individual Calibration Weights and Weight Sets
 Made of durable stainless steel and available in your choice of tolerances from ASTM Class F to Class 1.  Used for testing and calibration services.
Calibration Weights are Certified Accurate
   ASTM Individual Calibration Weights and Weight Sets
Built to the demanding specifications of the widely recognized and nationally acclaimed American Society for Testing and Materials (ASTM), these devices offer solutions for various classes of weights and mass standards used in laboratories across the country. They provide an optimal solution for businesses within the United States looking for weights that carry national recognition. 
Individual Calibration Weights with Statement of Accuracy or Certificate of Traceability
   OIML Individual Calibration Weights and Weight Sets
These weights are built to the exacting standards of the Organization Internationale De Metrologie Legale (OIML), a worldwide, intergovernmental organization with the primary objective of harmonizing the regulations and controls applied by various national metrological services. If your business has international implications, the designs and tolerances associated with these devices will be recognized in every facility, regardless of its location in the world.  If you are unsure whether to use ASTM or OIML specifications, OIML provides international recognition as well as a growing presence within the Western Hemisphere.
All the Calibration Weights You'll Want - With the Tolerances You Need for Testing and Calibration Services
   NIST Individual Calibration Weights and Weight Sets
Commonly associated with such terms as "field standard weights," "test weights," "tolerances," and "weights and measures inspection," these weights are designed to the specifications in NIST H-105-1, Class F, revised 1990.  They are typically used by weights and measures inspectors, as well as scale technicians for calibration services such as installing, sealing, and periodically inspecting commercial scales and weighing systems that are Legal-for-Trade certified under the auspices of NIST H-44.

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2. Choosing the Correct Weight for Your Application

    The first question you must ask yourself when purchasing any test weights is:

     "Do I want to be able to calibrate my scale or simply verify that the scale is weighing accurately?" 

    If you want to be able to calibrate your scale, you need to know the maximum capacity and the readability of the scale (or balance).  It is generally recommended to use a weight that is as close to the maximum capacity as possible and with a tolerance (see accuracy classes for mass standards) of at least 10 times the smallest displayed increment of the scale.  Also keep in mind that quite often a balance will only accept a specific mass standard for calibrating purposes so it is a good idea to check the user manual for the recommended calibration weight to use.  If you don't have the manual you can also call Algen Scale Technical Support Dept at 1-800-836-8445 and we will advise you of the correct weight to use and calibrating procedure if needed.

    If you simply want to use the weight to test your scale from time to time to make sure it is accurate then choosing a mass equal to the typical weight you put on the scale is often a good rule of thumb.  For high capacity scales such as floor scales which can weigh up to several hundred pounds or more, one or two fifty pound weights ( 25 kilograms) is recommended.  Also keep in mind the strength of the person who will be using the weight:  a 50 lb weight is about the maximum that a healthy man can lift whereas a female employee will typically be more comfortable with a twenty pound weight (10 kg) or less.  Algen Scale will also be pleased to advise and recommend the best test weight for your needs.  We also carry various carts for transporting or storing your weights. Call us at 1-800-836-8445 or email: .

    Once you decide the denomination and number of weights required you still must choose the classification (i.e., Class 1, 2, 3, 4 or F).  For this you need to review the next section called, "Accuracy Classes for Mass Standards and Test Weights."

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3. Accuracy Classes for Mass Standards and Test Weights

    Accuracy class of weights is defined as a class of weights that meets certain metrological requirements intended to keep the errors and uncertainties within specified limits.  For example, a Class 1, 1000 gram weight has a small tolerance of +/- 0.0025 g while a Class F, 1000 gram weight has a larger tolerance of +/- 0.1 g. This value is also referred to as the uncertainty of the weight. 
For complete listing of weight tolerances click here
Requires Adobe Acrobat Reader - Free Download .

    The following chart will help you define the type of weighing equipment you have and which corresponding class of weights would be appropriate:


  Typical Use

 Recommended Weight Class

  Primary Laboratory Reference Standard - High precision standard used primarily as a reference for calibrating other weights.

 OIML Class E1

 ASTM Class 0

  Precision Analytical Balances - Used to calibrate special precision analytical balances with a readability as low as 0.1 mg to 0.01 mg, Classes I and II. 
Can be used as a reference standard in calibrating other weights.

 OIML Class E2

 ASTM Class 1

  High Accuracy Balances - Working standard for precision analytical work,
built-in weights and external weights used to calibrate precision balances with a readability as low as 0.01g to 0.001g.

 OIML Class F1, F2

 ASTM Class 2

  Top Loading Balances - Appropriate for calibrating balances with moderate precision, with a readability as low as 0.1g to 0.01g.

 ASTM Class 3

  Industrial and Commercial Scales & Balances - For use with retail, wholesale and commercial scales; industrial scales; dial scales; even pan balances; platform scales; postal scales.  Also used for Class IIIL and IV Weighing Devices and for calibrating scales in Legal-For-Trade applications. Brass or cast iron commonly used materials in weights, although also available in stainless steel.

 OIML Class M1, M2, M3

 ASTM Class 4, 5, 6

 NIST Class F

* see also, Weight Tolerances Chart  Requires Adobe Acrobat Reader - Free Download Here

    Algen Scale is available to assist you in choosing the best weights for your application and budget.  Also inquire about how to save money by ordering weights in a set rather than individually. Call us now at 1-800-836-8445 or email us:

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5. Choosing the Correct Certification

     By now you have chosen the denomination and number of weights you require.   You have also decided whether it is more economical and/or convenient to purchase individual weights or weight sets.  And you have determined which class of weights would be suitable for your weighing equipment by referring to the Weight Tolerances Chart and the General Guidelines Chart.
    Your next step is to select which weight certification you require (if any at all). The next three questions should assist you as well as the Weight Calibration Certification Guide which follows:

Question #1: YES NO
Do you need NVLAP accredited laboratory certificate or report to meet ISO/IEC 17025 and ISO 9000 requirements? NVLAP Certificate Go to Question # 2
Question #2:    
Do you need traceability to NIST? Traceable Certificate Go to Question # 3
Question #3:    
Do you need serial numbers on your weight(s) or weight set(s) ? Statement of Accuracy
with Serial Number
Statement of Accuracy



 Statement of Accuracy  This document states that the mass (weight) has been compared to a known   standard.  The standards used have traceability to NIST and the certificate will list the nominal value, description of weight(s) or weight set(s), material, class and tolerance. This is neither a traceable nor accredited document.
 Statement of Accuracy
 with Serial Number
 Same as Statement of Accuracy above, plus a serial number is included on the weight(s) or weight set(s) and corresponding certificate.
 Traceable Certificate  Includes all the information on the Statement of Accuracy with Serial Number plus: this document includes actual weight values as well as uncertainties and tolerances.  Traceable to NIST. The uncertainty to tolerance ratios are not guaranteed. This is not an accredited document.
 NVLAP Certificate  This document conforms to ANSI/NCSL Z540-1 and includes all the necessary information that is required by the superceded Military Standard Spec 45662A.  The following information is provided: nominal and correction values, tolerance for the specific class, assumed density and the environmental conditions present at the time the tests were performed. Weights that include this certificate are traceable to NIST. This is an accredited document.

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6. A Brief Historic Overview

Weights have been used over the centuries as a reference standard for determining the value of raw materials and goods usually for the purpose of trade and commerce.

In ancient times, commonly found materials were often used such as grains, seeds and stones.  A rudimentary even balance was constructed and the weight standards (seeds, for instance) were placed on one pan and the material in question was placed on the other pan.  When the two pans were even, the seeds or stones were counted and that determined the "weight" of the material.  Today there are still remnants of these origins.  We still weigh diamonds and gemstones in "carots," which was derived from the carob seed.*  And gunpowder is still weighed in "grains" (one grain equals 0.06479891 grams).

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7. The Need for Standardization

As trade and commerce expanded and civilization spread it is easy to understand the many problems that would arise and how the demand for more standardization arose. 
Through a series of royal edicts, England by the 18th century had achieved a greater degree of standardization than the continental countries. The English units were well suited to commerce and trade because they had been developed and refined to meet commercial needs. Through colonization and dominance of world commerce during the 17th, 18th, and 19th centuries, the English system of measurement units was spread to and established in many parts of the world, including the American colonies.*

However, it would take clauses in the Articles of Confederation (ratified by the original colonies in 1781) and the Constitution of the United States (ratified in 1790) giving power to the Congress to fix uniform standards for weights and measures for the U.S. to achieve its own standardization.  Today, standards supplied to all the States by the National Institute of Standards and Technology (NIST) assure uniformity throughout the country as well as compliance with the international community at large.*

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8.  Links for Additional Information

*Sources for this article and for additional reading and information:

For the history of U.S. Weights and Measures Standardization:

For the history of British Weights and Measures Standardization:

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Toll-Free: 1-800-836-8445

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