This summary (link was taken down on nist website) was done several years ago but it brings up some good points regarding checking truck scales for accuracy and storing tare weights for trucks.

The concept of storing a tare weight for a particular truck sounds like a great idea and a wonderful time saver but as you can see from the presentation, it can lead to some very inaccurate weights.

Stored Tare
Stored and recalled from memory in digital indicators and computers.
Charts with truck-id and tare weight taped to the wall.
Marked on vehicle or driver information.

What Changes Tare Weight?
Driver/Passengers on-off truck
Repairs or modifications to vehicle (e.g., new tires, paint, welding etc.)
Tools, material handling equipment, personal effects.
Fuel and other fluid levels.
Mud, dirt and others (e.g., product retained in bed of dump truck).