2002 9.9 4-Stroke Idle Speed Adjustment

[fishnazi]

In order to adjust the idle speed, the Johnson service manual for my 2002 9.9HP 4 Stroke Model J10R4SNF indicates attaching "the engine tachometer to the spark plug high-tension wire". I'm not familar with a tachometer that attaches to the spark plug wire - does anyone have any info on this type of tach?