Answer:
What you do to determine the length of something
What is the middle of water but is not an island?
What goes up and down but never moves?
Round and round I go never stopping in a continuous flow. I hang out with numbers each and every day and nothing ever gets on my way. What am I?
White and thin, red within, with a nail at the end. What is it?
If itβs information you seek, come and see me. If itβs pairs of letters you need, I have consecutively three. What am I?