Why do particle counter results vary in aerosol particle counters? Paul Dozoretz of Particle Measuring Systems (PMS) talks to Patty Fabian regarding several scenarios including matching data from identical particle counters (same make from same manufacturer), matching similar particle counters (similar critical specs, different manufacturer), and matching different particle counters from different manufacturers (hint: don’t try it!). Understanding this will help you better understand your instrument data and what it means.