C. Tape Calibration

1. General

a. When is a 100 foot tape exactly 100 feet long?

The material characteristics of a tape lead to systematic errors when it is used. These errors can be eliminated by procedure or computation. However, to do this requires tape calibration to determine its length under specific conditions. Knowing how much use conditions differ from calibration allows error control or compensation.

b. Primary conditions

(1) Temperature

Changing the temperature, Figure C-1, will cause a tape to shrink (cold) or expand (warm).

 Figure C-1
Temperature Effect
(2) Pull

Insufficient pull (tension) will not stretch out the tape sufficiently, too much will over stretch it, Figure C-2

Figure C-2
Pull Effect
(3) Sag

 When the tape ends are held up with no intermediate support, Figure C-3, its weight will cause sag, drawing the two ends closer together.

Figure C-3
Sag Effect