In copending application Ser. No. 144,225, filed Jan. 15, 1988, invented by Kenneth Paul VonBargen, and assigned to the assignee of this application, there is disclosed a particle measuring instrument of the general type to which the present invention is directed. As disclosed in the above-identified copending application, particles entrained in a fluid are measured by passing a beam of light through the fluid stream, detecting the resulting light forward scattered from particles passing through the light beam to generate pulses and determining the amplitude and the length of the resulting pulses as measurements of the particle sizes.