Abstract: A device for use in checking and/or calibrating the accuracy with which a blood constituent concentration measuring instrument is operating. The device includes a capillary tube size member having annular bands marked on its outer surface. The bands are of predetermined axial extent and simulate centrifuged blood cell or other constituent layers. The axial dimension of each band is measured on the instrument which provides a visual indication of corresponding blood cell count. The blood cell count indicated by the instrument is then compared to the known blood count corresponding to the predetermined axial extent of the particular band measured. This device may be used to calibrate the instrument or determine the accuracy with which the instrument is operating.

Abstract: A method and apparatus for rapidly changing the spatial modulation imposed on a stationary light beam to conform to a preselected one of a multiplicity of discrete character symbols. Automatic orientation tracking is provided which establishes a fixed direction for the spatially modulated light beam that is independent of the character accessed and provides a fixed position for the character image. The technique may be employed in electrographic high speed printers and has particular utility when used with standard character generating template masks for character generation, though it is also effective when employed with a holographic generating mask array.