Calibrating the SWR/forward/reflected watt meter on an MFJ-941D Versa Tuner II

There are three calibration points for the combination SWR, forward watts and reflected watts meter on the MFJ-941D. Immediately behind the meter on the circuit board there are two variable resistors (potentiometers or pots) which calibrate the "level" of the meter for low and high power settings. (The high power setting one is closest to the outside of the case.) They are relatively easy to calibrate, you just transmit power through the antenna jack and out the external dummy load jack (if you have one, or through an antenna if you don't) and calibrate the 941D's meter to a known good meter (on your radio or inserted in-line between the radio and the tuner). Adjust the pot until the meter is correct. Tune high power and low power separately. Theoretically, if you tune it correctly for forward power, reflected power should "just work". BUT, sometimes you need to adjust the forward/reverse ratio by adjusting the variable capacitor that is between the two blue/black diodes near the current transformer (toroid wrapped with fine wire that the transmitter line passes through to the circuit board). I find it easiest to adjust this capacitor until the SWR on the MFJ's meter matches that if a reference meter. [You can use the tuning knobs to adjust the SWR up and down to make sure that both meters hit the zero point simultaneously--for use as a tuner, the zero point of SWR & Reflected watts is key.] I found that I needed to measure this with the metal cover installed (no need to insert screws), and only lift the cover up when adjusting the capacitor, so you can't just adjust it continuously while transmitting like with the power level adjustment pots. After you are happy with the F/R ratio (by adjusting the capacitor) you may need to fine tune the low/high power pots. For checking reverse power, you can either hook the radio up to the dummy load jack and the dummy load up to the transmitter jack (i.e. reverse the direction of power flow when you transmit), OR, if using a badly tuned antenna that has significant reflected power, you can use that instead. [If you are lucky enough to have a 100 ohm dummy load with a perfect 2:1 SWR, that also makes things easy....] Overall, I found that a $30 SureCom meter had better lower end sensitivity near zero than the 30 year old MFJ meter, but I was able to get them in sync enough that the MFJ meter would hit zero at the same point as the "reference" meter, just with a wider "dead band". https://youtu.be/IKdMe0cLGLM