I have one of those Hobbico tachs and like it bunches. It has changed the way I tune engines. For the high speed I set the engine to max rpm and then open the needle richer until it drops 300 rpm or so. That's it. A richened out setting that is fast to set and easily repeatable. I love it.

Set the high speed needle first (the big one that sticks out the carb)

Low idle is still trial, error and fine adjustments as always. Run at high throttle for three seconds, drop to low (I have idle-down and throttle cut switched programmed into my 9C), then gun it. If it cuts out suddenly richen the low end (back out the little screw in the carb barrel) and start over (always run high rpm between low end adjustments to get the fuel flowing). If it stutters and hesitates then picks up lean (clockwise) the low end needle.

Life is good. You can still do the pinch test (and not a bad idea) as a secondary check.