First of all I'm trying to use this symbol in a drawing which Solidworks online help says is the GOST Symbol in English but that doesn't bring up anything for me outside of their help page. I think it's flattened length but I can't be sure as I only know the German, Gestreckte Länge.

Anyway my Question relates to wanting to use this line to calculate the Overall length of a pipe before bending and I was Looking for a way for SolidWorks to calculate this. At the moment I've overriden the primary value but if the part changes in the future I would like this number to update. I've read somewhere about calculating from the surface area of the pipe and using the overall volume to get the length but how would I add those values into the Dimension text if I at all could?

Any help is appreciated.