The 1823A and 1856D are reciprocal 2.4 GHz and 3.5 GHz frequency counters that are microprocessor controlled. Their LED displays can provide up to nine digits of resolution using an external time base with a 10 s gate time. The high accuracy, sensitivity, and versatility of these counters make them an extremely valuable instrument to scientists, engineers, and communications technicians for a broad spectrum of laboratory and service applications.