Roger, it's not a rotating arm and float. The float is donut shaped (ie hole in the middle) and it just slides up and down the shaft with the fuel level.
I thought I would have to setup the sender correctly and then adjust the gauge to suit at empty/quarter/half/full, but it really was just 'plug-and-play' with no adjustment required whatsoever on my MGB fuel gauge.
Most impressed
Cheers,
Glen