TBH I have used multimeters and other meters made by Gunson for a very long time.
Needed them to do points dwell and to act as a rev counter back in the days when only sports cars or limos had a revcounter!!
Needed a revcounter to do the ignition timing. As well as my "tachostrobe". Never did get an exhaust gas analyser to do the mixture with. They weren't cheap nor were they very accurate. I do have one of those things you put in place of the spark plug to look at the colour of the flame inside the cylinder, again, only worked properly with a car whose carburettor wasn't worn.
And who remembers doing "plug cuts"!!!??? Also a carb balancer. Although some people swore they could do it by ear. With a tube.
I am of course aware that I am talking double dutch to quite a few members on here!
Do remember some of those Gunson products , years ago they seemed to be in every car shops , motor factors etc
Never heard that before ref a tube , remember I had to get my carbs balanced by a garage for my triumph 2500s
Talking of tachostrobe these were the ones I remembered