fuel gauge

[sportscott]

I have just replaced my instrument cluster for one with a rev counter original from a 2.0l dohc, I only have about 6 or 7 litres of petrol at the moment in the tank as run on lpg. the fuel gauge on the replacement was reading just over half, as is the fuel gauge on the Mondeo petrol 2.5l that was supposedly for a Transit, and all the other secondhand clusters I've seen for sale all seem to have the fuel gauge in this position. After fitting my instruments the gauge rose up a little. my fuel level sender is in order so question is, do I need to reset the gauge somehow or will it do its self after tanking it full to the brim? which I will do here in PL and take the petrol to Norway to use in my Outboard often wonder if I'm actually saving any money due to higher gas consumption carrying the weight but every little helps