Since these are largely hand crafted pieces, you don’t need to be incredibly precise - but my notes are for record purposes. While the dimensions are specific within the context of sun/bu/rin there’s always going to be some variance based on human error or preference.
You should only measure the flat of the shamisen - where the skin would be applied. The bevel or curve of the body is not counted.
I have attached an image dug up from the net to better illustrate what I’m talking about.
