Lock Point Entry Fields
Lock an individual field in a collection of fields that accepts multiple components from a single point entry (for example, the U coordinate, V coordinate and N coordinate for a point).
A field which accepts multiple values from point entry has a 
button next to it. If the button is clicked, the 
button indicates that the field maintains its current value and will not be updated during
point entry.
Figure 1. The
button
indicates that the point entry field is unlocked.As an example, use point entry to enter the coordinates of a point in the 3D view as the base corner of a cuboid. Lock the X coordinate and Y coordinate and
use point entry again to enter a different Z coordinate.