measuring rpm

I've gotten hold of a Actron multimeter that has an RPM setting and a clip-over inductive lead. Do I simply clip this over a plug wire? Or the coil wire? Will it display RPMs directly or do I need to multiply/divide/whatever? Any other hints?

Thanks,
Jerry

Actron has the user manuals available on line-here is link to one model

http://www.actron.com/cgi-bin/web_store.cgi?page=cp7678.htm&cart_id=4552917_7212

Did a quick try last night, but I hooked it up and the reading was weird. It wouldn't give a reading in the normal range of 0-3000. I had to set the switch to RPMx10 and then it would read something like 1800 - not something outside that 0-3000 range. I think I had the clip going in the right direction and far enough away from other wires.

So I remain confused,
Jerry

Number of cylinders shouldn't matter because a 4 cycle engine will turn two revolutions per spark regardless of how many cylinders.

It's real tough to use on diesels, though.

I had my whole response written with a few paragraphs devoted to 1,2,4,6 and 8 cylinder "differences" when I finally came out of the ozone and realized 'hey, wait a minute...'

Glad you relieved me of thinking I was alone.