Ruler app with different scales selectable. Both units system available: metric (meters) and imperial (inches and feet).
App contains mainly scales for model trains:
*0 (both 1:45 - US and 1:48 - Europe)
*00 - British scale 1:76.2
*H0 - 1:87
*TT - 1:120
*N - 1:160
*Z - 1:220
There are also scales used in different scale models (plane, ships kits etc.):
*1:43
*1:72
*1:144