watchis. I omitted it from my previous list of important and useful commands because I rarely use it. But today I had George open on the bench and was finding out what fan connectors on the motherboard corresponded to which speed sensor, as reported by lm-sensors.
watch -n 0 "sensors w83793-i2c-0-2f | grep fan"
Then, as I plugged and unplugged a 3-wire fan here and there, I could see on screen what was going on. This is especially important, cause you don't want to unplug the CPU fan for any length of time.
FYI, the sensor:fan port mapping for a DSBV-DX is as follows: