Characteristic result variation

[[Br...]]

Hi, I have a part where I have measured a plane ( normal to X & Y axis ) and a single point in the Z axis. When I go to characteristics to find a distance from the plane to the point I get a value of .0460, but if I go from the point to the plane I get .0446. Why the different values when I am using the same two features just switching which is specified first?
Calypso software.

[[To...]]

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Typically, the 2nd feature is the datum reference. However, I've seen some issues between cylinders and planes.

[[Br...]]

Thanks Tom, I will keep that in mind

[[Am...]]

Im gonna take a guess and i think its due to the alignment. Which distance characteristic are you using? The plane is going to read from the center of the plane, doing it one way might be using the plane as the reference thus the measurement is from center of plane perpendicular to plane up to that height, and the other might be a straight distance from plane center to point.

[[Br...]]

Using Cartesian co-ordinates for both measurements. The base alignment is to another plane which checks parallel to my measurement plane within .0001 or less.

[[Ma...]]

This is like Tom said - 2nd is datum reference - so if it's a point then axis are given by real touch direction. But i don't have it tested on points touched on chamfers and angled planes. Theoreticaly it can give good results, but just interpolated by deviations of nominal and actual a1 ,a2.

But almost everything can be simulated with theoretical features.

[[Me...]]

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I avoid Cartesian distance like the plague. It can be highly misleading and doesn't account for orientation of the considered feature.

[[Ma...]]

Trully - using caliper distance allows you to choose coord sys. and you don't worry about which point will be considered with plane for ex.