Abstract: A data decoder is provided which is useful for decoding data magnetically encoded on a magnetic stripe on the back side of a credit card which may be manually moved through a reader at a variable velocity. The data is decoded by comparing the occurrence of voltage pulses after the onset of a bit interval, representing binary data encoded as magnetic flux changes, with a preselected portion of the measured time duration of the preceding bit interval. If a voltage pulse occurs after the onset but before the end of the preselected portion, the data is determined as a binary "one"; if a voltage pulse occurs after the end of the preselected portion, the data state is determined as a binary "zero".