About Reference Entity Options for Distance
In measuring distance, some types of reference entities can be measured in different ways when you use reference entity options. To use an option, select the check box in the Options column next to a reference entity in the Measure dialog box. You can also set the measure_ref_option_status configuration option to specify whether the reference entity options are automatically selected.
Option
Description
Use as Plane
Extends the selected surface or plane to infinity in both directions only for the purpose of measurement. The surface remains the same, but it is treated like a plane. The measurement is the distance between the plane that would be formed by extending the surface to the other selected entity in the normal direction.
Use as Line
Extends the selected straight edge or curve to infinity in both directions only for the purpose of measurement. The curve or edge remains the same, but it is treated as a line. The measurement is the distance between the line that would be formed by extending the straight curve to the other selected entity in the normal direction.
Use as Center
Measures the distance from the center of a circle or an arc-shaped curve or edge. Clear this option to measure from the edge instead of the center.
Use as Axis
Measures the distance from the central axis of the cylindrical surface. Clear this option to measure from the surface instead of the axis.