The calibration of beam attenuation meters by means of a water standard measured with a two-pathlengths device is discussed. It is shown that the particulate scattering to attenuation ratio can be assumed to be constant to the same accuracy that the shape of the volume scattering function can be assumed to be constant in sea water. This observation allows one to correct beam attenuation meters without the need to measure forward scattering. An equation for this correction is derived and a table of values for the correction at a wavelength of 665 nm is given. The principles of construction as well as potential errors and their corrections are shown fora reflecting tube light absorption meter. Preliminary results for such a device are also shown.