Use arithmetic functions in VDEF definitions

[human]

In the current version only the following operators can be used in VDEF variable definitions: MINIMUM, MAXIMUM, AVERAGE, LAST, FIRST, TOTAL, PERCENT, LSLSLOPE, LSLINT, LSLCORREL. I would like to be able to use basic arithmetic functions like +,-,*,/ in a VDEF definition as well, so that I can do something like:

VDEF:delta=mydata,LAST,mydata,FIRST,-

Then I can use the delta variable in a GPRINT function to display its value in the legend.

Thanks, Ben van Balen