Tachometer and Hour Meter

[proturbo]

I bought a new Tachometer and Hour Meter,I was woundering to set the tacometer (spark plug firing revolution) There are 3 settings ,which one do I set it on for reading my RPM 1)-spark plug fires twice per revolution 2)-once perrevolution 3)-every other revolution:doah:

 

[smoky]

I think it would be every revolution, but someone else that knows for sure will post...
try it

 

[65ShelbyClone]

Every revolution.

 

[nitrosteve]

i have have the same one and if i remember the every revolution one is right