Device for measuring the length of a path.

摘要

A device which, when used to trace out a path on a surface provides a measure of the length of the path (e.g. for measuring the distance between two points on a map) comprises means (1) for dispensing a marking agent as the device traces out the path, and means (M, 2) for monitoring the dispensed marking agent. In a preferred form of the device the marking agent is deposited on a surface (S) as it is dispensed, and a property of the marking agent (e.g. when the agent is electric charge, its polarity) is changed each time the device has traveled a predetermined distance, the monitoring means counting the number of changes.