Related historical trivia: the old Minox "spy" camera http://en.wikipedia.org/wiki/Minox came with a metal carrying strap that had smooth spots spaced out on it that looked pretty nice. In reality those smooth spots were calibrated in close focus distances to match the controls, you could quickly and efficiently "step on the chain" (i.e. hold the chain down with your finger) and shoot documents in good focus and minimal shake.