The Measurement tool is used to measure distances on the screen using a Reference Length as its basis. The construction is the same as for a Line Segment. If no Reference Length has been constructed yet the Measurement has no way of measuring the distance so the construction will be cancelled. Note that the measurement is accurate at the scale of its construction. If the Measurement path is rescaled, the value will be no longer be valid. The only other option available when constructing a Measurement is whether to use the same paint that was used for the Reference Length Segment segment (the option is called “Unit Paint”) or to use the currently selected painted (called “Current Paint”). Here’s an example: