I believe it works differently. The speed signal from a fan is simply a train of 5 VDC pulses (2 per revolution). When they arrive at the mobo header the system counts the pulses in a fixed time period and calculates the RPM from that. If you send two or more pulse streams from different fans into that counting circuit, it receives twice as many pulses. IF they were all clearly separated, you'd get a reading that is the sum. BUT the two pulse trains are never exactly the same in frequency, so the pulses shift in and out of "sync". This means that some pairs of pulses overlap and get counted as only one, and this phenomenon keeps changing all the time. The result is that the actual reading produced varies widely, from very low to nearly...