Calculation of tolerance for Position of a Cylinder

[[Ju...]]

Hello everyone! 

I stumbled upon the following highlighted option while calculating the position of a Cylinder with respect to datum ABC with material conditions (Datum A is a Plane, Datum B is a Cylinder and Datum C is a slot). Does anybody know what this option really mean? If I select it, will the calculation of the tolerance for a different feature that has the same datum system impact this calculation? (We have a couple of other features with the same position calculation with respect to the same datum feature control frame). 

When I select this option, sometimes the value of the position will drastically change (~200 um) or sometimes the calculation will simply not compute. Let me know if I can give more details to explain my situation. 

Thank you!

 

[[Ch...]]

Yes, if this option is selected, all tolerances, that share this datum system, are computed as one big pattern. This will, as you observed, impact the result. To get any result, all the checked features may not violate their linear size tolerances, and the virtual gauge has to "hit" every feature; if one of these prerequisites i not met, the tolerance stays not computed.

Background: A datum system under material requirement does not have a fixed actual location, as it may use the free space around the virtual gauge to better accommodate the checked feature. So for different tolerances, different locations may be optimal. If the "compute tolerances together" is not checked, these different optima are used for each tolerance.

In real assembly situations, this independence is not given: There is only one final assembly situation, and all checked features have to conform to it. This is simulated, when "compute tolerances together" is checked. This case is actually the default in the ISO GPS standards, in a rare exception from the usual independence principle.