It is about a wind-velocity measurement digital circuit in an exam question. Here is the link where you can see the circuit: http://www.diskusjon.no/index.php?showtopic=752114&hl=+temperaturm%E5ler Its norwegian but you can see the circuit if you scroll down on the page. Well anyways the question is pretty simple actually: The 7 segment display is showing 00 even though the wheels on the wind-velocity measurer are rotating. What are the possible reasons for that??