Standard Model
*Used on engines with one spark firing on each  
  revolution of the crankshaft.
*1 cylinder 2 stroke (reads 1x / revolution) Briggs,
  Kohler and Honda type engines.
*4 stroke with electronic ignition and no points.
*2C can also be used on 2 cylinder engines where
  the cylinders fire 1X per revolution.

Note 1: Engines frequently referred to as a "4 stroke" may not be a true 4-stroke because they fire on the exhaust stroke as well – requiring a 2C.
Note 2: You reset, hours accumulate.