Cheers guys, I think we all agree on the forces at play and also that people who don't fly aircraft generally don't understand what it is that pilots are doing and therefore are not well equiped to make decsisions about how long we can fly for before it becomes a safety hazard.
That is what I like about the idea proposed above. It is fairly black and white and hard to argue with the results of a simple test. I am sure many people have had the idea before me as it's quite a simple one but right now, with the ground swell of opposition to dangerous F&D regulations, I would like to know whether a)something similar has already been trialled.
b) in your opinion, it would work if mandated
c) it would save lives and money