See also Gauge block Golomb ruler Perfect ruler References http://www.luschny.de/math/rulers/prulers.html http://oeis.org/wiki/User:Peter_Luschny/PerfectRulers http://www.iwriteiam.nl/Ha_sparse_rulers.html http://www.maa.org/editorial/mathgames/mathgames_11_15_04.html http://www.contestcen.com/scale.htm http://members.cox.net/wnmyers/sparse_rulers.txt Number theory Combinatorics Length, distance, or range measuring devices