The Countess® Test Beads are an accessory to the Countess® Automated Cell Counter. Their purpose is to aid the user in testing their instrument to ensure that it is properly counting and sizing the samples. The Countess® Test Beads are latex beads with a nominal diameter of 10 µm ± 10% and are suspended to a concentration of 1 × 10^6 beads⁄mL ± 10%.