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Field Inspection Manual — Non-Automatic Weighing Devices

Part 3, Section 24: STP-24: Weigh-in/Weigh-out Systems — Vehicle Scales


Sections 31, 33 and 55 of the Non Automatic Weighing Devices Specifications.


A weigh-in/weigh-out system is typically a vehicle scale in which an inbound truck is weighed either loaded or empty, the inbound weight is stored, the truck is then emptied or loaded as the case may be, the outbound truck is weighed and the larger of the two weights (outbound or stored weight) is printed as the gross weight, the other printed as the tare weight and the difference computed as the net weight. Inbound weights, recalled weight values, and gross, tare and net weights must be identified to clearly document the transaction. The storage, recalling, and printing actions are limited so that they do not facilitate fraud.

This system does not retain inbound weights when the outbound weight is printed. The client's file (where inbound information is stored) is cleared for the next transaction.

In many cases, auxiliary equipment such as computers (software) are used to perform weigh-in/weigh-out operations. The following minimum requirements are essential to ensure that the system will not lead to measurement errors and will not facilitate the perpetration of fraud. Inspectors ensure that weigh in-out systems meet the requirements when the device is initially inspected.


  • Any inbound weight values must be recorded and automatically identified as such. If inbound weights are not printed at the time the weigh-in operation is performed, the inbound weight information must not be lost during a power interruption.
  • The gross, tare and net weight values must be recorded (printed) in an automatic sequence when the outbound weight value is obtained.
  • The recorded weight value is not required to be automatically identified as a gross weight value, provided that the other two weight values are clearly and automatically identified as net and tare.
  • If a device can indicate and/or record in two and more weight units, all gross, tare and net weight values shall be automatically recorded in the same weight units. This condition must be met regardless which weight unit is being displayed.
  • Any weigh-in/weigh-out weight values stored in the memory register shall automatically clear and not be retained in memory after a complete transaction of gross, tare and net has been recorded.
  • Any recorded weighing value from the memory register shall be automatically identified and defined.
  • Tare values shall not be stored as negative values. (Negative numbers shall not be accepted).
  • Keyboard tare entries shall not be accepted into weigh-in/weigh-out memory registers.
  • If the system is equipped with a tare memory register for weighing gross, tare and net weights separate from the weigh-in/weigh-out feature, the tare weight shall not interact with the weigh-in/weigh-out feature.
  • The data processing system performing the weigh-in/weigh out operation shall only accept weight values when the scale indicator is in the gross weight mode, or give an error signal.


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