Heliotrope Smith wrote:

The white digits are hundreds of cubic feet and the red digits are tens of
cubic feet so the moving red counter will revolve 10 times to increment
the white digit by 1.

The test dial records 1 cubic foot of gas per revolution and this is used
to determine the gas rate of the appliance under test.

The text below the digits on the meter says that it's 0.071 ft^3 per
revolution which makes it 14.08 revolutions per ft^3 so that's about 140
revolutions for one red digit.

--
Mike Clarke