Timing Light Accuracy

There are possible errors in timing lights. The trigger mechanism for the flash can introduce delay. A flash tube is supplied a voltage of a few hundred volts by a charged capacitor, a third connection provides trigger at a few thousand volts.

A scope with two channels can be used to measure delay between the real ignition event, and photo transistor signal resulting from flash event. Delay error increases with RPM.

Inexpensive clamp-on lights are often polarity sensitive at the clamp. Clamps are typically marked to show side that goes to plug. Incorrect clamp, results in failure to trigger, or significant error.