had to be known! The set square proved to be required to calculate the total size of the object: First measuring all the sides, which were then scaled up to fit the viewing distance. Everything was taken into account: Rotation, slant and axis, to come to the correct conclusion, using all the measuring aids the tool offers.
A drawback came afterwards, when everyone found out that the set squares were inaccurate, leading to inconsistencies. Dependency upon a tool, which you are unable to check for accuracy is a dangerous thing!