This button allows the setting of metric or inch units for the current drawing session. All the Router-CIM variables that depend on units are updated to this selection. If a drawing already exists, the units are predefined. You can change the unit settings, but they will not agree with the settings of the original drawing. The metric or inches setting in NCVARs is not affected. In other words, changing this setting will not scale your drawing, but only change the default units that the post processor reports when making NC Code.