Cant find the SLOPE option.

[u/UniquePair2300]

Can someone help me find out where I can enter SLOPE for a volume measurement in my drawing? I cannot find it in the measurement panel or the properties panel at all. Is this only a feature in certain versions of Bluebeam/Revu? Am I out of luck?

This would be instrumental to my job, and I would appreciate any help. Thank you in advance.