N14HK
I agree, but this is common practice, if the Cessnas are those without a step on the (whatever you call the wing support member) so a ladder is needed, and nobody is bothered to bring one out. When I moved to PA28s I saw 2 cases of a virtually empty tank when there should have been "3 hrs" in it. But low wing planes are easy to check.
Beagle
"In the absence of reliable fuel gauges, a totaliser would seem to be the best solution. So long as it also has a non resettable scale."
I am not sure if there is a tamper-proof one for GA, and the popular Shadin costs far too much to find its way into anything much other than brand new £200k planes. And I still had a case of the FOB figure being tampered with (upwards) by a CFI who borrowed the plane... (not kidding!). He made the mistake of incrementing it past a plausible range, and I had the EDM700 data to check it against (and that cannot be tempered with). Actually, an EDM700/800 with the fuel option would give you a tamper-proof fuel flow LOG, although.... the problem is that somehow you have to set the FOB (fuel on board) figure when you fill up, and that always gives you an avenue to fiddle it, or make a mistake when not filling right up... But a Shadin etc is probably essential if you rent a plane out dry.
I agree with all you say, but such calculations just cannot be done reliably. You've always got to start with a physical check, without it everything you do is worthless no matter how many times you check it.
Chilli Monster
"Just out of interest I wonder how much the "Fill it up" brigade do Weight & Balance calcs"
Depends on the plane, a TB20 you can fill up every time and with 0-2 average passengers and some luggage you will always be OK. I've played with a W&B calculator for it and it's very hard to move it outside. This is also generally true with a PA28 and 1 average passenger, though I was often told by the school to not fill it right up (which I always ignored). Of course it can be argued that any plane which can carry fuel fuel and full passengers is a sub-optimal designl!!
Hairyplane
I am sure you've tried this, but if the FAA has given an STC for the EDM700 for an N-reg plane, the CAA often respects that. Alternatively there is the Shadin, which does not involve fitting all those thermocouple probes... But I have got through a few Shadins in 1 year, like a lot of American avionics they are awfully unreliable. You might have to pay a CAA Level 2 firm to get the approval done for you; there is one in Bournemouth and also Air Touring at Biggin Hill might be able to do it. Cost... maybe £1000.