@idefix37 Thank you for the explanation. Now I understand!

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@idefix37 Thank you for the explanation. Now I understand!

@idefix37 With the sider all the way down, windy shows isobars (isolines of pressure) at sea level.
With the slider moved up to 500mb, I expect windy to show a chart of isobars (isolines of pressure) representing conditions in the mid- troposphere. This level is at an altitude of approximately 5,500 meters (18.000 ft), relative to a standard atmospheric pressure of 1013.25mb at sea level.

Windy does display this chart, if geopotential height is selected. The isobar labels then represent pressure as equivalent altitude in feet.
Not much use to a sailor. I want to know how to display isobar (isolines of pressure) values in mb instead of feet.
Here is an example standard 500mb (500hPa) chart from ECMWF.

https://stream.ecmwf.int/data/gorax-blue-009/data/scratch/20201120-0600/a0/render-gorax-blue-009-6fe5cac1a363ec1525f54343b6cc9fd8-Z3CX9u.png

Great, thanks. How do I display pressure isobars at 500hPa labelled with hPA value instead of height .

1. Moving the altitude slider to select, say 500mb isoline view does not display a 500mb isoline chart.
2. Most times the isoline labels will show the new barometric pressure, but not always.