Measure that Mate (Why are results different?)

I was recently asked,

“I did a check where the distance mate value and the measurement for the same features shows two markedly different values.  Have you ever seen anything like this?”

Distance Mate Result

This individual wondered how it was possible that his measurement of two associated features was different than the dimension he entered for the distance mate assigned to those two features.

Measurement Results

My reply was pragmatic.

“Without seeing the model directly, it’s hard to confirm the error.  However, I have found that whenever SolidWorks gives me a number and it doesn’t make sense, it is due to something the user is doing or some misinterpretation of the data.  This causes me to try to investigate when such issues arise by first considering what the user is doing.

“In this case, I’m assuming you are measuring from the center of the circle to the flat face.  However, I notice that your mate is set up face to face. I’m guessing SolidWorks is mating your hole based on the closest point of the circular face, and not the hole’s center.

“To fix this, use the temporary axis of the hole as the selected entity for your mate instead of the hole’s face.”

This individual followed my advice and was able to eliminate the apparent discrepancy.  In general, it is a good idea to check look at how SolidWorks (or any software) functions in order to understand why something is happening.