About 43 years ago I had a fuel exhaustion forced landing in an Aeronca
Sedan (15AC) on floats. It had simple plexiglas sight glass gages that
went directly into the two wing tanks - and me thinking what could be
more reliable?

What I didn't know is that it had nylon fuel cells rather than rigid
tanks. It also had leaky fuel caps and a partially plugged vent system
that allowed the fuel cell to collapse in the air. The sight glass
gages showed a comfortable half full until about 5 minutes before
complete fuel exhaustion. I landed in a swamp, drifted to shore, found
the farmer etc...... He was surprised.

In my 172M, I stick it with a Fuelhawk and never let planned landing
fuel get below 1 hour. But, I still don't really know if that hour is
really there or not except that it has never taken more than 33 (of 39
useable) gallons.