|SpeedFan makes assumptions based on the hardware monitoring chip it detects on the mboard.|
It assumes sensors are connected to all inputs - on some mboards not all of the inputs have sensors connected to them - in that case, SpeedFan's reading is incorrect and it never changes. In other cases, the mboard maker did not connect the sensor to the correct input specified by the chip maker.
If SpeedFan detects a hardware monitoring chip, then almost always you can go into the bios Setup and find the current readings listed in the bios - the readings for inputs that are not hooked up to sensors will NOT be listed there, and what reading is for what will be correct, even if the mboard maker didn't connect them to the chip manufacturer's spec input. Also, the bios has almost always been tweaked to make the readings as accurate as they can be.
In other words, if there are temp, voltage, and rpm readings in the bios, don't bother using SpeedFan unless you tweak it to not show invalid readings (no sensor is hooked up) and adjust the readings so they're ~ the same as in the bios.