Comment by danso

Ah that makes sense. I was thinking it from the wrong way -- i.e. the way Calvin's dad explains how they discover the weight limit for bridges -- no need to test from small to minimum-amount-needed when there's a certain, reasonable volume of blood that pretty much works all the time (and I'm assuming that's been tested to some degree). Though I'm still surprised blood-drop-variance wasn't just something studied frequently out of scientific curiosity and because it seems relatively easy.