Hi Bryan!
There is a lot to be said about this function.
Just a couple of things that can cause problems for you :
UMESS have normally (depending on version) 2
methods for best-fit. Gauss is using least squares mathematics that "evens up" the deviations. This method can result in a situation where a pattern of bore holes that are in tolerance after the original measurement, are "best" fitted out of tolerance when AD 137 is used!
The other method is Tchebycheff.
This one minimize the deviation but compared with nominal position and not compared with tolerance zone. This will result in an measuring error if tolerance zones for the features are of different size, such as when maximum material principle applied.
You must also be aware of the fact that maximum material condition applied on datum is calculated wrong in the software.
Example : Let's say we have 2 holes with true position tolerance and a center hole as datum. Zeiss 300 software adds difference between actual dimension and maximum material dimension to the tolerance zone when using best-fit (and also in other cases). This is correct if deviation from true position on the two holes are in the same direction but if one is placed with X- and one with X+ deviation you can not use any tolerance from datum, regardless of datum size!
As I said, there is much to be said and if you have any specific questions please feel free to send an e-mail :
vcecmp.kjka@memo.volvo.se

Best regards
Karl-Johan Karlsson
Volvo CE CMP
Eskilstuna SWEDEN