# Why is H always* the letter used to describe the level of a barrier?

A quick and (hopefully) easy question. Why?

*(always / often / when it's not B)

• Is that for real? – Kiwiakos May 23 '16 at 11:36
• @Kiwiakos as in is it a real question? Yes! i'm curious. – will May 23 '16 at 12:24

I do not have any reference, but I think $H$ is for hitting.