Common Instrumental Errors in Linear Measurement in Surveying

Length other than standard

Tape manufacturers do not guarantee 100 ft steel tapes to be exactly 100.00 ft. An error due to the incorrect length occurs every time the tape is used.

Temperature other than standard

Steel tapes are standardized at 68° F (20° C).

A temperature higher or lower will change the length of the tape. Temperature of the tape can be quite different from the air temperature measured.

Tension

If tension is greater than standard the tape will stretch. If less than standard tension is applied the tape will be shorter than standard.

Sag

A tape not supported along its entire length will sag. By applying correct tension the sag can be reduced.

Poor alignment

This error occurs when one end of the tape is off-line or there is an obstruction in-line. The actual distance will be less than the measured dis

Faulty marking

This error is random as the result of incorrect placement of chaining pins. Careful placement of chaining pins and then checking the measurement will reduce errors.

Incorrect reading or interpolation

The error occurs when reading or noting the measurement clearly or in a hurry. Careful reading and using a small scale to determine the last figure will reduce errors.

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