Duke Scientific Corporation's new COUNT-CAL™ is a cost effective and convenient product for validating particle counters. Packaged in single-use bottles, and intended to be sampled directly from the bottle, it eliminates the need for serial dilutions and extensive sample handling, thereby minimizing contamination. The particles are suspended in an ultraclean diluent and the concentration is optimized for use in light obscuration particle counters and other low concentration counting applications. The particle diameters are traceable to the Standard Meter through the National Institute of Standards and Technology (NIST).