OK! I just Googled the word mensuration, then cut and pasted it below;
Mensuration is the branch of geometry that deals with the measurement of area, length, or volume in 2D and 3D shapes. The 2D shapes can be drawn in a plane like square, rectangle, triangle, circle, etc..
I also Googled; mensuration geometry in measuring instrument string length. That stated pretty much what I stated. Bottom line it geometry (measuring). LOL!