Tacho, for tuning?

[subanator]

I want to measure my RPM for testing purposes and really want to use a tacho off the coil primary side or inductive pickup type.
Problem being that the only off the shelf tools I can find are pricey automotive multimeters and old school dwell meters that are not too accurate or robust.
Most are 4,6 or 8 cylinder ranges, how do you get it to equate to a single cylinder? Does anyone know what the factor is to read a single?
I did find a handheld clamp type one but at $85 is a bit hard to read when its under the tank when riding the bike.

Otherwise the kits through Jaycar or Silicon Chip are requiring a 12V power supply.

I am interested in what others have tried or can suggest?

[T250K]

 The Husqvarna chainsaw dealers over here use a small tacho to set high speed fuel mixture when servicing their chainsaws.   It's battery powered, can't remember whether AA cells or 9 Volt.    Pickup is inductive off the plug lead, and the digital readout could be strapped to the bars, or maybe even hung off the peak of your helmet.    

I was given one years ago but have moved fifty years worth of treasure since then so finding it could take an airport dog.     If you don't manage to get one, ( I'm guessing other brands of chainsaw probably use something similar )  let me know.     Cheers,    T250.     

[asasin]

You will probably find the kitset ones will run off a 9 volt battery , then you can put in a box and mount to bars. I use my mates Kart setup when I need to.they work really well and have a max memory etc.