INCRA Miter 2000 - Manual (Page 7)

ABOUT YOUR FENCE SCALES
7
Fig. 15
Align scales using
optical window
All Incra products use overlapping 16" long Lexan scales. The
overlap allows fine-tuning the scale from one end to the other
to agree with the high degree of accuracy provided by the
Incra saw toothed positioning racks. These scales are printed
initially in 16" lengths (0-16", 16-32", 32-48" etc.). As they are
slid into the scale slot on the fence, the ends are overlapped
and aligned using the optical window located at the end of the
second scale. Fig 15. The friction fit will keep the scales in
place. If you wish, you can use a small piece of double faced
tape at the overlap to ensure that the scales move together
when changing your zeroed setups for mitering.