I have a coil of tubing that I need to solve for the oal of it.  I have defined a new custom property oal.  What I need is to take the mass properties value and divide it by the weight per foot of the tubing.  Very simple.   Is there a way to do this in the custom properties?   I tried number and text but neither seems to work.   I was able to make a global variable and do the math but this does not show up in the custom properties when I open it.  I have many configurations so the value has to calculate each time.   Global variables scares me as well.