# Reference Length

The Reference Length tool allows you to specify a unit length that can be used by the Measurement tool for measurement. The segment is constructed in the same way that a Line Segment is constructed. When the construction is completed, a dialog box will be presented asking you to specify the length of the segment. The default is 1 but you can enter any positive value that you want. You can have more than one Reference Length. The currently selected one will show an asterisk beside its number, and it is this reference length that is used for any future Measurement values. You can change the selected Reference Length using the Switch Reference Length tool. Here’s an example: