Tach location

this is the place where ive just fitted my tacho (its in a 78 aspen) ive tidied up the wiring now and taped over the hose clip, i cant seem to move the little red pointer? when i do move it, where should i set the limit at, the engine is a standard 318 smog motor, sorry the picture is a bit blurred, also i noticed theres quite a few of these sunpro tach ll gauges in this thread, are they a good gauge?