Hartzell POM and Logbook No. 115N
Hartzell POM and Logbook gives the instructions for the low pitch stop adjustment on page 403, 404, and 405 under Testing and Troubleshooting. It specifically states that RPM adjustments must be made with reference to a calibrated tachometer.
I had to tweak mine and it really wasn't that big a deal as long as you follow the instructions in the manual.
C.(1)(a) states "Loosen the jam nut while holding the low pitch stop with an allen wrench to prevent the low pitch stop from turning as the jam nut is loosened. Turning the low pitch stop IN will increase blade pitch to reduce RPM, and turning the lowpitch stop OUT will lower blade pitch and increase RPM." In addition, "Turning the stop 3/4 of a turn will change the blade pitch of approximately one degree. One degree of blade pitch will change engine RPM by approximately 140-150 RPM. One full revolution is equal to approximately 200 RPM."
Please consult the Hartzell Manual, follow the instructions, and you should be fine. I think the main thing is to know that your tach is giving you the correct reading. The props usually are not off that much.