Tolerance Selection ­ Metric and Avoirdupois Weights

• Metric Tolerance Summary Chart
  Metric Tolerance Chart ANSI/ASTM & NIST
  Metric Tolerance Chart OIML
  Metric Tolerance Chart Old NBS Classifications
• Avoirdupois Tolerance Summary Chart
  Avoirdupois Tolerance Chart Pounds
  Avoirdupois Tolerance Chart Ounces

QuickLINKS:
> What mass tolerance should you select?
> Troemner manufactures and calibrate weights to meet or exceed
the highest tolerance standards of ANSI/ASTM, OIML and NIST.
> Weight Applications

 
What mass tolerance should you select?

It is Troemner's recommendation that a mass have a tolerance that is 1/3 to 1/4 of the readability of the device you are verifying or calibrating or 1/4 of the accuracy you require for your application. There will be instances where the tolerance of even the most precise class of weight will not be 1/3 to 1/4 of some balances or applications. For these applications, we recommend that a calibration certificate be purchased with the mass so that the user as opposed to just knowing the allowable tolerance of the mass will know the error of the weight.

Some users try to apply the 1/4 tolerance to balance readability and end up selecting an ASTM Class 0 or OIML Class E1 mass. Although these weights are the finest available, unless these weights are maintained under strict handling and environment conditions, they will not maintain their tolerance. These classes of weights are used as primary reference standards for calibrating other reference standards and weights. Because of the extremely tight tolerances, it does not take much use, handling, or poor environmental conditions to cause a weight to change it mass value.

 
Troemner manufactures and calibrate weights to meet or exceed the highest tolerance standards of ANSI/ASTM, OIML and NIST.

ANSI/ASTM E617:

Standard Specification for Laboratory Weights and Precision Mass Standards

Mostly used in the United States, this specification covers various classes of weights and mass standards used in laboratories ranging from Class 0 to Class 7. Tolerances and design restrictions for each class are described in order that both individual weights and weight sets can be chosen for the appropriate applications. This specification also recognizes OIML R 111 that describes classes E1, E2, F1, F2, M1, M2 and M3.

OIML R 111:

Weights of Classes E1, E2, F1, F2, M1, M2, M3

This international document describes the physical characteristics and metrological requirements of weights that are used for the verification of weighing instruments, for the verification of weights of a lower class of accuracy and with weighing instruments. This document includes a recommendation for seven classes of weights in tiers of uncertainty.

NIST:

Specifications and Tolerances for Field Standard Weights

These specifications and tolerances are specific for reference and field standard weights (NIST Class F). Reference and field standard weights are used to test weighing devices where the weight of the item is required to determine the item's price. This document sets minimum requirements for standards used primarily to test commercial or legal for trade weighing devices for compliance with NIST Handbook 44. These devices include but are not limited to delicatessen scales, jewelry scales, postal and parcel post scales and dairy product scales. This specification permits the use of a weight at its nominal value in normal testing operation, where the tolerance on the item under test is at least three times as great as the tolerance of the weight. This Handbook also specifies the design, marking, adjusting cavities, and density of these weights. Any variation in design from Handbook 105-1 must be submitted to NIST for approval. More information on these weight specifications is available in Troemner's Mass Standards Handbook.

 
Weight Applications

In order to select the appropriate weight for your laboratory, you must first determine exactly how you intend to use the weight. Your unique application will help determine exactly which Troemner weight will suit your needs. The following guidelines explain the applications of the different classes of weights:

• ANSI/ASTM Class 0 – Used as primary reference standards for calibrating other reference standards and weights.
   
  
• Troemner UltraClass – Available exclusively from Troemner, these weights were developed to meet the most demanding calibration needs with the ability to be adjusted. Troemner UltraClass weights are the most precise two-piece weights available with weight tolerances 50% greater than ANSI/ASTM E617 Class 1 tolerances. Troemner UltraClass weights combine high precision with the advantage of two-piece construction (1 g and larger) avoiding costly replacement issues associated with one-piece weights. Troemner UltraClass weights and weight sets are available in a full range of weight denominations.
   
  
• ANSI/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 0.1 mg to 0.01 mg.
   
  
• ANSI/ASTM Class 2 – Appropriate for calibrating high-precision top loading balances with a readability as low as 0.01 g to 0.001 g.
   
  
• ANSI/ASTM Class 3 – Appropriate for calibrating balances with moderate precision, with a readability as low as 0.1 g to 0.01 g.
   
  
• ANSI/ASTM Class 4 – For calibration of semi-analytical balances and for student use.
   
  
• ANSI/ASTM Class 5 – For student laboratory use.
   
  
• ANSI/ASTM Class 6 – Student brass weights are typically calibrated to this class. This class also meets the specifications of OIML R 111 Class M2.
   
  
• ANSI/ASTM Class 7 – For rough weighing operations in physical and chemical laboratories, such as force measuring apparatus.
   
  
• 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 IIIL or IIII, and scales not marked with a class designation.
   
  
• 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 0.1 mg to 0.01 mg.
   
  
• OIML Class F1 – Appropriate for calibrating high-precision top loading balances with a readability as low as 0.01 g to 0.001 g.
   
  
• 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 is commonly used for student brass weights.

ANSI/ASTM Style Weights

OIML Style Weights