Abstract: The reflectivity compensating apparatus is utilized in a dual wavelength spectrophotometer wherein a chopper mirror, having alternating mirror segments and open spaces equal in area, cuts through a light beam from a light source and the mirror segments reflect light through a liquid sample in a sample container to a photodetector having an output channel. The reflectivity of each mirror segment varies slightly from the other segments.

Abstract: The cover is made from a sheet of transparent plastic material and has a generally annular shape, i.e., the general shape of a flat ring, which is easily received over an annular rotatable sample tray having a plurality of sample cups therein. The cover has a horizontally radially extending projection adapted to engage a post on a table top supporting the sample tray to prevent rotation of the cover and an annular shoulder on the underside of the cover which fits around a circular envelope defined by the radially outwardly disposed top side edges of the sample cups in the sample tray and which engages the top side edges of the sample cups to prevent horizontal movement of the cover as the tops of the sample cups frictionally engage the underside of the cover and exert a moment force on the cover when the sample tray is rotated. The cover also has an opening therethrough for allowing liquid sample to be inserted or withdrawn from a sample cup when such sample cup is in registry with the opening.