(those aren't mine, and the asking prices are nuts.)
I've got an extra unit; might have to dig around to see if I have any of the diesel probes and stuff. I use it for gasoline engines; no probes needed except the magnetic wand and the inductive pick-up.
Times diesel engines based on the flash of combustion--a light (luminosity) probe takes the place of one glow plug, and magnetic probe senses position of damper.
Times gasoline engines based on inductive probe sensing spark, and magnetic probe sensing position of damper. Does what a timing light does, only with more style.