Checking of the opacimeter. The zero and full scale checks must be made in the opacity readout mode, since the opacity scale offers two truly definable calibration points, namely 0 per cent opacity and 100 per cent opacity. The light absorption coefficient is then correctly calculated based upon the measured opacity and the LA, as submitted by the opacimeter manufacturer, when the instrument is returned to the k readout mode for testing. With no blockage of the opacimeter light beam, the readout must be adjusted to 0.0 % ± 1.0 % opacity. With the light being prevented from reaching the receiver, the readout must be adjusted to 100.0 % ± 1.0 % opacity.
