MCC scrive:

Is there a good reason why isobars on a surface pressure chart are
spaced at 4 mb? I would have thought 5 mb spacing would have made more
sense. TIA

I have no idea of the correct answer, if there is one, but it would seem
possible that 4 was selected because it is a third of a dozen (or a fifth
of twenty) and the original measurements would have been 'imperial'
rather than the more 'metric' 5. Just a wild guess.


--
Gianna
Peterhead, Scotland