First, each flight deck fuel quantity indicator sends a one wire resistive signal to a relay. This signal is called the rebalance signal, I think. This relay is controlled by the SPR master switch. When the SPR master is off, the rebalance signal for each gauge goes to a summation unit. The summation unit, located in the left hand hog troth, has a pot for each tank signal that is adjusted during the totalizer calibration. Each of the pot output signals are added together. The output from the summation unit goes to the total fuel indicator. When you turn the SPR master switch to any other position than off the relay energizes and sends the rebalance signal to the SPR fuel gauges, so you can refuel the airplane and not have anyone in the flight deck. When the SPR gauges are working, the totalizer is inop and the "SPR ON" light on the fuel panel comes on. And that's it, I hope this sheds some light on the totalizer thing.
