Jeremy Handscomb wrote:
When we consider the dam air values we are talking about the thickness of
the layer between 1000mb and 500mb. It is measured in decimeters (tens of
metres) such that 10dm (or dam) = 100m or the famous 528dm = 5280m (or just
over 5 kilometres).


Actually *decameters* and the simbol is *dam*

dm is decimeter, that is 1/10 of a meter.