National Coal Board  N.C.B. Metric Methane Calculator

National Coal Board  N.C.B. Metric Methane Calculator

Metric Methane Calculator.
National Coal Board N.C.B. metric methane calculator.

Made from plastic and brass with a P.V.C wallet. Size 6″ inches diameter.

It has four revolving calculating discs on the front and one on the back.

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