My numbers are more accurate with the 80/63 than the 47/37.
And most sets of gears should have a 20 and 21 tooth gears in them.
I posted that because I am sure that 20, and 21 tooth gears should be
cheaper, more accuarate and easier to find than the 47 and 37 tooth
gears,
If someone wants to go that route.

Pete