Why would you see rpm on the meter? Not a very useful measurement.
Tuning idle speed on carby.
This. And the point about a wasted spark is true, which is why a multimeter that takes that into account is a better option when all you need is the rpm, vs calculating it from the frequency. I have a contact tachometer that I can easily use on a "lawnmower" engine on the bench, but if I'm working on a motorcycle, scooter, moped or any engine on a "vehicle" I may not have easy access to the crankshaft even for a non-contact tachometer. Ironically, I have no use for an automotive multimeter for working on cars, mainly off-road equipment (hence why I put quotes on "vehicle"), so the higher cyl. ranges are not needed. I don't want to have to disassemble my'81 Honda Passport scooter engine, for example, just to measure what the rpm is, and no it does not already have a built-in tach, all it has is a speedo.
Edit to add: All due apologies to the OP, I did not mean for this to take your thread on a tangent. I was hoping you had the specs and if you knew what the minimum # of cylinders is for this meter. BTW, I cannot find this meter anywhere, even a website that purports to be Lucas's.