Chain and tape

Measuring distance directly with a chain or tape is the oldest survey method and is still used for short distances, building set-out and checks. Steel tapes of 30 or 50 m are standard; fibreglass tapes are used for rough work and offsets; metric chains of 20 or 30 m with links survive mainly in teaching and land records. Chain surveying, which builds a network of triangles from measured sides, suits small, open, fairly level areas.

Careful taping needs ranging, to keep the tape on a straight line between stations using ranging rods, and attention to slope. On sloping ground the tape is either held horizontal in short steps or laid along the slope and the horizontal distance computed from the slope angle or height difference. Offsets, measured at right angles from the chain line to features, locate details such as walls and trees. An optical square or the 3-4-5 rule sets right angles.

Taped distances carry systematic errors that can be corrected: the tape's actual length differs from nominal (standardisation), temperature differs from that at which it was standardised, the pull differs from standard, the tape sags between supports, and slope. Random errors come from marking and reading. For precise work, all corrections are applied. In modern practice, electronic distance measurement in total stations has replaced long taping, but a tape remains the quickest independent check on site.