Well, I would post this in the TIPS & DESCRIPTIONS section, but there isn't one (yet?). I have put this here in the CODE section since it will not 'disappear' from the list as fast as in the Pcdmis section, i just copied it over:
GAP ONLY
Gap only acts like a SNAP POINT for edge points. When doing edge points, ESPECIALLY on sheet metal, you SHOULD be taking a surface sample hit so you can control the depth of the hit on the edge. There is shear and breakage on the edge of sheet metal, you SHOULD be touching on the shear portion.
To enable you to do this, time after time after time, WITHOUT changing the program, use a surface sample hit and the proper depth (small value if the shear is on the 'top', a value = (stock thickness - a small amount) if the shear is on the 'bottom'. Once you determine the proper depth to hit the shear everytime, you need to ensure that the CMM knows where the surface of the part is, that is what the surface sample is for.
To report the edge point, you CAN do XYZ & T and T will give you the (T)otal amount the edge point is off nominal by, along the edge vector. HOWEVER, if using surface sample hits, the XYZ values will NOT jive with the "T" value. I almost always (99.995% of the time) will report the "S" axis at the same time, this gives you the SURFACE deviation (like the "T" of a vector point) as well as the (T)otal edge deviation and eliminates the need to also take a vector point (2 for 1, eh?).
IF you want to report JUST the trim edge itself, you can use GAP ONLY (in the FEATURE LOCATION dimension window. What this will do is allow you to use the surface sample hit so you can control the depth of the edge touch, but it will then 'project' the actual point BACK INTO THE NOMINAL surface and then report the XYZT of the edge point AS IF THE SURFACE CHECKED ABSOLUTELY PERFECT, thus giving you only the GAP, as if you were doing a feeler check to a hard gage.
It sure would be NICE if there were a section set up for this kind of thing. If the TITLE described EXACTLY what the post was dealing with it would make it MUCH easier for newbies to find QUICK easy help (since the search don't work so well). This could be the first such post in a TIPS and DESCRIPTIONS sections