Correction Due to Incorrect Tape Length
During a period of use, a tape will gradually alter in length for a variety of reasons. The amount of change can be found by having the tape standardized at either the National Physical Laboratory (NPL)
for invar tapes or the Department of Trade and Industry (DTI) for steel tapes, or by comparing it with a reference tape kept purely for this purpose. The tape may then be specified as being 30.003 m at 20◦C and 70 N tension, or as 30 m exactly at a temperature other than standard.
Corrections in Taping
Taping operation is done to determine an unknown length or for the purpose of laying out a required specified length. Corrections to taping are applied by the use of the following rules:
Measuring
• When measuring out lengths with a tape that is “too long”, corrections are added.
• When measuring out lengths with a tape that is “too short”, corrections are subtracted.
Laying out
• When laying out lengths with a tape that is “too long”, corrections are subtracted.
• When laying out lengths with a tape that is “too short”, corrections are added.