Timing Light

The timing light is a specially designed strobe light.
While the timing light is connected to the number 1 cylinder spark plug, the timing light will flash each time the ignition system "fires" that plug.
The flash is used to illuminate the timing mark which appears to stand still during illumination.
Timing light connection to the spark plug is usually of the inductive type, which senses secondary voltage passing through the plug wire.
Another type of connection is the in-line connector. Both types of connectors provide accurate information, but the inductive type is somewhat more convenient.