tachometer calibration

[wounded minnow]

I have a 1988 90 H.P. Johnson Outboard which I recently installed a tach. I am getting some weird readings. The needle will show 5300 RPMs and hold for a while and then keep rising. I have been told there is a calibration adjustment on the tach. itself, but I'm not sure where. I don't have the original instructions any more. Any help would be greatly appreciated!

Thanks.

[Valv]

There is a small round wheel in back of tach, you have to use a small screwdriver.
here's Teleflex web site support, it's very handy:

http://www.tflx.com/tech.html