Abstract: A voltage controlled frequency source has an output frequency which varies in accordance with primary power line frequency variations. The output frequency of the voltage control frequency source is used to control the rate at which data is fed into a teleprinter machine thereby providing the teleprinter with data at a rate that can be varied in accordance with power line frequency variations. A method of modifying input data rate into a teleprinter machine in accordance with frequency variations of the primary power line frequency is also provided.