There are multiple settings on the back of the instrument to set the digital RPM readout for different HP engines. With it set to default it showed me 5500rpm at idle, so I adjusted it to show 700-900prm at idle but I am only getting 3800rpm at WOT and I should be getting 5500rpm.. The instruction have a diagram for the different settings but the are set by the number of "alternator pole pairs" and I don't know how many I have, that's my question.. Dummies lol