Scale test car

Image:Scale test car CN 52285.jpg|thumb|right|A Canadian scale test car owned by Canadian National
A scale test car is a type of railroad car in maintenance of way service. Its purpose is to calibrate the weighing scales used to weigh loaded railroad cars. Scale test cars are of a precisely known weight so that the track scale can be calibrated against them.

Purposes

Cars are weighed for various purposes. These include:

Axle load limits

Cars are weighed to ensure they are within the axle load limits of the railroad.

Customer billing

Cars are weighed to determine the amount of cargo loaded. This is used to bill the railroad's customers for the carriage of bulk commodities, so it is essential that the track scales be accurate.

Construction

Many scale test cars were small, old railroad cars carrying heavy metal weights as their superstructure. Scale test cars needed special handling so they would not suffer damage, which might alter their weight. They were reweighed periodically on accurate scales at the railroad's shops.