This is kind of a unique one, looks like they were using it as 

some type of counting unit? 

The marks on it go from 10 to 22 with 2 marks that are not numbered 

If anyone out there knows how this was used please let me know and Thanks! 

Ratio is 25 to 1

Nice used vintage Gear Electric Motor Speed Reducer unit Looks like the counter plate with numbers and the sprocket can both be removed held on by set screws.
Input shaft size 5/16" Output shaft size 5/16 inch
Overall height 4-1/8"
Base plate size 3" x 4-1/4"

Grand Rapids, MI 49534