Q. The batch plan dialog has an 'expressions' page, usually containing feature and instrument names.  What is it?

A. The Expressions tab in the Batch Plan dialog is really just an expansion of the Data Source box in the Features tab.  Every feature has an expression associated with it and this tells QS-Pro where the data for that feature will come from.  Usually it is just a single instrument so the expression looks something like...

  Ftr1=Caliper

The bit after the equals sign is what you see in the Data Source box.  If your feature is a little more complex than that then you may want to type in an expression consisting of several instruments or other features.  You can calculate a diameter from two opposing probes for instance - use an expression like...

  Ftr1 = Probe1 + Probe2 + 25.5

...where 25.5 is the diameter of the reset master than the probes were reset against.  You can still type the Probe1 + Probe2 + 25.5 bit into the Data Source box if you prefer and it will have exactly the same meaning, but expression can get very complex (look at application notes CAN-201 and CAN-202 to see how complex) and then the extra space in the Expressions tab comes in handy.  It's also the only way you can make expressions spread over several lines, or create intermediate variables.

The expressions tab has a page for each measurement set in your batch too and expressions in one set can refer to variables in another - tho you need to be careful of the order if measurment if you do that. 

The QS-Pro manual and help files contain extensive coverage of the power of expressions and also give full istings of the mathematical and trigonometric functions built into QS-Pro.