Made for gasoline engines used on the Vanguard, and Surveyor hovercraft, such as Kohler and Briggs and Stratton. Also works on Rotax, Honda, Yamaha etc. If it sparks this will count it. Specially made for Amphibious Marine with long length of coaxial cable. You can just extend or you will get crazy readings.
Other lengths available on request. 3" wide x 1 1/2" tall x 3/4" thick. The digits are 5/16" high and reads to 9999 rpm. The "fixed" model in stock work with common engines such as Briggs or Kohler, that spark once on each revolution of the crank shaft. The "Select" model is adjustable in case you are not sure. It can work for engines that spark with every rotation of the crankshaft and up to 8 sparks per rev. In other words; Adjustable from 1 spark per 2 revolutions to 8 sparks per revolution, works on most gas engines. The battery lasts for approximately 7-10 years, then it is toast.