The sample is measured in a compression cell, giving excellent reproducibility and minimising sample errors. The basic specification is ± 0.5 %.

This one is in good condition and works well.

The circuit comprises an ingenious modification of Wheatstone's bridge in which the specimen forms one arm. The two calibrated moisture controls form the ratio arms. The fourth arm comprises an auxiliary bridge in which three arms are resistive and the fourth consists of a thermionic valve. The out of balance voltage of the main bridge is applied to the control grid of this valve; the resulting out of balance current is indicated on a centre zero meter.