Tach setting?

[ugly duck]

I have a 79 55hp and bought a new to me old console that has an older det mar tach in it , does anyone know what setting number the tach should be on to read the rpms accurately for my motor? Thanks for any input. The console came off of a 77 model boat that had a 110 or 115 johnson motor on it and would the tach be on the right setting already?

[boats.net]

Most all the older ones used a 10 pole setting on tach.