The universal tape measure.
I would consider this as a tool not much unlike what a fisherman would have in his tackle box for making sure the fish caught is in legal limits. It can be used for a number of purposes but I mostly use it for measuring seat tube and top tube lines.
Small enough to be able to fit in a pocket like a Zippo lighter; I am able to take it with me quite easily.
Accurate measurements are necessary when measuring a client’s current ride for determining the geometry of their future dream machine.
My background is in engineering, measurements are critical.

Jalon Hawk