Clarke-Hess Communication Research 2510A-S1055 Upgrades standard Model 2510A Phase Angle Voltmeter with improved specs: Phase Accuracy - 10Hz to 2KHz 0.02, 2KHz to 5KHz 0.03, 5KHz to 10KHz 0.04, 10KHz to 50KHz 0.05; Phase Resolution - 0.001 degrees; Adds IEEE-488 capability.