Issue creating formula in block

[rchiasson]

I've been fighting with building a formula in a block utilizing a field from another block. I have a support steel member that once placed, will be lengthened. I need a distance from center of the pipe to the top of concrete. I created a block with a field referencing the insertion point (center of pipe) it works fine giving me this elevation. I also have another block that is the datum node. I have several fields in this block, and it is located at the bottom of the support steel plate. I am trying to create a field that takes the center of pipe elevation and subtracts the datum node elevation to get a distance. I created the formula referencing the COP elevation field and the elevation of the datum node. The information shows properly where I am building the formula, when I click evaluate, the Preview gives me ##### and when I create the datum node block that is also the output I get. I can't figure out why it won't give me the difference between the two elevation fields. I don't know what I can do differently to have that information in the datum node.

[tcorey]

You might consider creating a LISP routine that does the calculation and stores it to a variable. Have the field that displays the distance access the LISP variable.

Tim