The Snap list is automatically enabled in the user interface when working with a Vector Point or a Surface Point feature. For a Circle feature, it is only visible if EnableCircleDCCSnap is set to TRUE in the PC-DMIS Settings Editor. In addition, since snap only functions well after a rough alignment, it is disabled until an alignment is established.
The Snap list determines whether or not measured values "snap to" the theoretical vector for a Vector Point, a Surface Point, and when enabled, for a Circle feature. This simulates a perfect machine staying exactly on the approach vector, not deviating by as much as a micron when measuring the point. If you set this to Yes, then the measured values snap to the theoretical vector with all the deviation along the vector of the point. This is useful for focusing on a deviation along one particular vector.
For example, suppose you want to measure the height (in Z) of a table's top. You don’t really care about your X and Y (secondary and tertiary) axis errors which can occur from machine drift (tunneling error). In this case, with Snap set to Yes, you will only be reporting the Z value. Any errors in X and Y will be ignored as the measured X and Y values will equal their theoretical counterparts.