If you need a quick ruler picker-upper, try electricians tape. Take a 4"-6" length and fold it in half part way: 1/4 + 1/4 stuck together, 1/4 stuck left and 1/4 stuck right. Fast and easy. And if it falls off, do it again.
(Thanks to a quilt show vendor who must remain anonymous because my brain is like a sieve. Even took a picture of her and her name badge! I am so sorry!)