After looking again at the picture, I think those NUMERIC displays are the same as the ones that used to be on gasoline pumps.
They are rotating geared dials with numbers around the periphery. Very much like the dials on radio gear in older private airplanes.
A single feed (specific impulse or voltage) goes to the first digit, and all the other digits are driven by gearing off the first digit.
The dials on radio gear were not a good example. My bad.
The Odometer on older automobiles would be the best example.