Faulty Fuel Economy Gauge

[phildg2000]

Why is it that my economy gauge needle sits WAAY to the right (out of view) when I'm at idle? It then starts to appear when I've hit around 50kph with light throttle. If I slow down a bit, it moves to the left or if I give it more gas, it moves to the left (I believe this is how it should behave). If I really step on it, it disappers to the left (normal movement I believe, but why disappear past the edge?). And then when at idle, again it's on the left side, out of sight. What gives?
All other gauges operate normally so I don't think it's a cap problem, or is it?

Thanks,
Philip
'89 525i euro 5speed

[dca]

actually, it calculates instantaneous consumption per 100 km. It is calculated from various sources. when you stop, because of not travveling over a distance, consumption per 100km is infinite, when you move slowly again it is close to infinity, becaus eof using so much fuel at lower gears, when you go faster it reaches to ideal rolling speed and consumption is optimized, whne you go faster and faster it faces to air drift and friction of surface, then consumption again increases. slowing is in reverse order. this is the normal way.