Abstract: An asynchronous to synchronous converter is disclosed which produces clock pulses in synchronism with data bits of a non-return-to-zero (NRZ) code having a variable data rate. The converter is established adapted for use in optical reading of the Universal Products Code (UPC) code symbol which is of bar code format. The converter comprises a high level bit clock system for clocking the dark bar bits and a low level bit clock system for clocking the light bar bits. A high level measurement circuit times the single bit dark bar pulses and sets the timing for the low level bit clock system and a low level measurement circuit times the single bit low level pulses and sets the timing for the high level bit clock system. The converter receives asynchronous serial data and produces a clock pulse for each bit of the data pulse so that the serial data may be decoded.