Digital multi blade tachometer. Specs: 1. It looks fancy and is compact in size, Very handy to use. 2. Multiply the readout by 10 for final rpm reading. 3. It measures 2-9 blades prop rpm. 4. It shows 4 digits in a 0-99,999 rpm range. 5. It comes with a replaceable 3V LITHIUM Battery. 6. There is an auto shut-off function (no signal detected in 5 mitutes). 8. It needs a little electronic power (20ua) when the TACH is not in use. This may prolong the life of the battery.