On 2013-05-17 12:26:36 +0000, Desperate Dan said:

On Thursday, May 16, 2013 1:11:13 PM UTC+1, MCC wrote:
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

--

MCC

It's an interesting question. When pressure was measured in inches,
isobars were drawn at 0.2 inch intervals and I thought thee may be a
correlation there but there isn't. Isobar intervals can be 2mb, 4mb or
8mb depending on the scale of the chart used so I suspect it's for that
reason. ( hectoPascals (hPa)is the correct term these days!)

I remember gradient winds being measured on a geostrophic scale in the
'old days'.

Could it be that a 4mb interval was deemed the most convenient spacing
(on a UK and Eastern Atlantic chart) for accurate measurement with a
pair of dividers that had a physical limit to how far apart they could
be opened?