Matco Tools MD44 Smartach Plus, used, for gas engines, 1,2,3,4,5,6,8,10 &12 cylinders, 2 & 4 stroke, reads RPM's and ignition pluse, tested, seems to work fine on 4 strokes, on some small 2 strokes the RPM's were reading at 4x what it should have been, it was tested on 1 cylinder engines.  Has a clean battery compartment, in box with instructions, some scuffs and scratches, has an ID mark on the back. Uses one 9 volt battery NOT included.