Eight methods of linear measurement

Eight methods of linear measurement are:

1. Pacing: distance = number of paces $\times$ average length of one pace. Rough, about 1/100 accuracy, used for reconnaissance.
2. Passometer or pedometer: a small instrument carried by the surveyor that records the number of steps.
3. Odometer, measuring wheel (perambulator): a wheel that records its revolutions; distance = revolutions $\times$ circumference. Used for road lengths.
4. Chaining: direct measurement with a metric chain (20 m or 30 m) for chain survey.
5. Taping: direct measurement with steel, invar or cloth tapes. Corrections are applied for high accuracy.
6. Tacheometry (stadia): the distance is calculated from the staff intercept between the stadia hairs and the vertical angle, using a theodolite.
7. Subtense bar method: a bar of fixed length (e.g. 2 m) is placed perpendicular to the line and the small angle subtended at the instrument is measured by a theodolite; $D = \dfrac{b}{2}\cot\dfrac{\theta}{2}$.
8. Electronic distance measurement (EDM) and total station: distance from the time or phase of electromagnetic waves. Very accurate and fast.

Additional methods: GNSS/GPS positioning, photogrammetry (from photographs) and LiDAR/laser scanning.