So here's your answer to your question.
I have owned both the Floscan 5500 and the Navman 3100 in twin engine
installations. (and, the Navman 2100, which is the apparent equivilant
to the Standard Horizon unit)

The Floscan, much to my disappointment did not allow you to set the
gallons remaining. Consequently, for it to be accurate in it's
totalizer in relation to your tank, you have to fill up every time. At
125 gals, and 275 gals for the last two boats, that's not always
practical. I would, however like the totalizer to be reasonably
accurate as analog fuel gauges rarely are. It's also a great way to
subtly get your freeloading friends to understand just how much you
are absorbing for their entertainment ;-)

The Navman units, besides being a digital display instead of sweep
movement, have many features that the Floscans either don't have at
all, or are only available on much more expensive units. For instance,
the 2100, and the 3100 do allow you to set the gallons added to the
current fuel remaining. The 3100 has a GPS interface that allows you
to display instanteous MPG (or GPM in my case). This calculation lets
me continously adjust my throttles, and trim as sea conditions, vessel
weight, and wind direction changes throughout a passage.

I have found the 3100 with twin transducers at less than half the cost
of a comparable single transducer unit from Floscan. The 2100 is
typically available with a single engine sender for around 150.00

Oh, and for diesel engines......
http://www.navman.com/marine/product...200/index.html

Sounds like I work for Navman. I don't. Just a happy customer that's
done fuel monitoring both ways.

BD wrote in message ...
I have a 2002 225 Merc EFI and want to hook up a FLO Scan (Series 5500)
or other Fuel Computer, like the Standard Horizion Fuel Flow meter or
the NavMan Fuel Flow meter.

On the FLOScan, I see the on the gauge it shows gallons, how does it
know , if say , you have 75 gal in the tank and add 45 more gallons. Is
there and way to adjust this? Same question for the Standard Horizion
and NAvMan.

They all show the GPH but im curious how the gauge knows how much fuel
is in a half full tank. Or do you just need to start with a full tank

On the FLOScan I gues I would need the 0-32 GPH. Anyone have a 225 Merc
EFI with some GPH numbers and rpm.

Thanks