A forward scattering spectrometer probe (FSSP) is an optical particle counter, suitable for counting and sizing particles in the size range of 0.5 - 47 micron diameter. It essentially consists of a laser, various optics, a photo-detector module, and electronics to process the data. The UMIST FSSP is a PMS FSSP model 100 with the DMT SPP-100 rev-1 electronics upgrade, and is configured for ground based use.