The surveyor had a standard chain to which the field chains were frequently compared. A correction was required to compensate for any difference between the standard measure and the tape used in the field. Because steel band tapes will stretch, a tension handle was used when chaining in the field so that the same tension (usually twenty pounds) was used as when the chain was calibrated.
The Society has both standard tapes associated with Alberta Land Surveyors and with Dominion Land Surveyors as part of their collection.
Tape, ALSA Standard
Tape, DLS Standard