1:24 Scale Rule
6 Inches Long

Also:
1:87.1 Scale
3" Long
1:48 Scale
3" Long

One side is 1:24 and accurate to one scale inch +/- 0.002".
The other side is 1:87.1 scale, accurate to three scale inches
+/- 0.002" and 1:48 scale, accurate to one scale inch +/- 0.002".