mine came in just a few days, pretty fast considering it came from china.
i don't have a way to calibrate mine yet. i just guess that idle is about 500 and redline is about 2700.
the dial stays in between the 2 mostly, but once it did read up in the 3000's. i let my foot off the pedal and than back on it again and it re-established at 2700.
there is a 3 way switch on the back of the tach to get it into the right range for the alternator, then there is a screw for fine tuning.
its close, well worth the $15. my next down hill run will will be more confident with the trans being able to hold a constant rpm number.