This product line offers a series of ready-to-use standards for validating optical particle counters with no dilution and handling. The products are suspensions of monodisperse polymer microspheres in water with a concentration of 2000 particles per mL. A magnetic stir bar is included in each bottle for clean, convenient and direct sampling by instruments. This series of size standards is provided for setting or checking the calibration of channel thresholds or for checking the count precision of liquid-borne particle counters. Their certified diameters are traceable to NIST. They are packaged as 100mL screw-cap bottles, sufficient for four or five calibration procedures on most counters. The microspheres are composed of polystyrene, which has an index of refraction of 1.59 @ 589nm and a density of 1.05 g/cm3. The aqueous suspension medium contains a combination of dispersing agents, which help to keep the particles from clumping or sticking to flow surfaces in the particle counter. The EZY-CAL™ product line meets all of the unique and demanding requirements of the contamination control laboratory in modern industries.