[Talk-GB] maxspeed field - what units should we use. etc

[WessexMario]

> you only need 5dp to get an exact mph->kph conversion anyway :-)

I think that's the big issue.

People won't be able to agree on whether we should enter 0, 2,3 or 5 decimal 
places, if anyone can remember or look them up correctly. And it's completely 
unintuitive thinking of speed limits with non factor 10 vaules with decimal places.

The accuracy for practical non-scientific use of the value is almost irrelevant, 
Journey times will vary more because of road conditions, speed cameras are set 
to a few mph above the limits, the legal requirement is for car speed to be 
measured to 10% accuracy.

The problem is someone is always going to enter the wrong values if it's done in 
kph, and we'll keep on having umpteen different values for what should be and 
exact figure, eg 30 mph.

The answer must be to have a solution that prefers 30,40,50,60,70 values in mph 
rather than (rounded or 5dp accurate) kph numbers,.