hairdye

Ok guys hope you can help
I fitted a different clock face today to show mph instead of kph, When i put it all together i dont know if i knocked the petrol gauge but it was showing empty. Ithought it would have gone to where the petrol level would be.
i took the clocks apart again and when i move the gauge by hand to a 1/4 tank it stays there, is this how these gauges work. I know when the ignition is off it normally shows whats left in the tank, do i need to set it at a 1/4 tank (thats how much is in) and then when i fill up should it work .
This is urgenty if you can help as the dash is in pieces and i neeed to be out in an hour .
cheers
wayne