maths

please tell me if this is possible:

I wish to assign 3 numerical variables to object (polyline). lets call them x1, x2, x3

Then i want to start autocad command that will calculate x3=x1-x2 and print result near the end of line.

could it be done in lisp or should i forget about it?

Sounds like a project for Lee Mac. Lee speaks with a lisp.

er, to be honest i need even more than that, something like this:

http://mfgcommunity.autodesk.com/blogs/blog/view/7/Tracing_Polyline-connected/

I have blocks and polylines that connect them. Each of the blocks can add or subtract a number (decibels) from starting point.

Some blocks split the line in two or more.