In a nutshell: A six-digit frequency counter with leading-zero suppression implemented entirely in NAND gate logic. Complete I.C. complement: 249 * 74HC00 quad NAND gate 1 * 74HC132 quad NAND gate with schmitt-trigger inputs 1 * 4011B quad NAND gate (used in analogue mode as the signal-input pre-amplifier) Measurement range: 1Hz-to-999,999Hz Gate period: 1s Display update rate: 0.5Hz (2s)