because this tach is supposed to be sensing the impulse from a single ignition coil running through a distributor, the waste spark/ non waste spark is a moot point. take the # of cylinders and divide by 2 to get the number of coil impulses per engine rotation (4 stroke) so for example, a v8 has 4 coil impulses per revolution to a 4 cylinder's 2 coil impulses. it goes without saving that a two stroke has a coil impulse for every cylinder per revolution.
SO, if the tach is set to 4 cylinder(4stroke) mode, then it will interpret the 1 impulse/rev. of a single cylinder 2 stroke as 1/2 of a revolution of a 4 cyl. 4 stroke (2 impulses/rev.)
IF the impulse were to be taken from a single plug wire of a multi cylinder 4 stroke with a waste spark electronic ignition (like virtually ALL modern vehicles) then there would be no difference in the number of impulses per revolution between a two stroke or four stroke engine, reguardless of cylinder count. this is how the trail tech tach works.
pretty fuckin simple in the grand scheme o things imho.