Hi Richard,
Thanks very much for your suggestion. You'd code does almost exactly what I'm looking for. I've taken the liberty of making a couple of minor modifications which (a) make the implementation a bit quicker to use, and (b) provide two alternative display forms. A notebook containing my modifications is attached. I've not carried out any rigorous testing yet, but, based on initial trials, the approach appears to work exactly as required.
Ultimately, it would, I guess, be easy to add more InputAliases for commonly used units. What might be neat solution would be a facility to enter esc-"Canonical Unit Name"-esc followed by the right arrow. So, for example, esc-"Meters"-esc (preferably without the "") would produce m in the input cell rather than the less conventional and horribly long-winded form Quantity[None,"Meters"].
I think you've solved a problem that's been causing me, and no doubt many other users, a real headache for some time and would suggest that this, or a similar, type of approach to units is built in to the system.
Thanks again for your input, its very much appreciated.
Ian
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