Abstract: The method of storing, without interruption, digital signals having asynchronous transitions and reproducing these digital signals upon an expanded time scale after the occurrence of a fault.The apparatus comprises an input counter, an output counter, an adder operated to subtract, and a latched gate by which the adder stops the output counter when the outputs of the two counters are equivalent. The least-significant-bit of the output counter comprises the output signal, which is stored in a register. A second register simultaneously stores an output from the adder which signifies that more than one pulse is stored in the input counter. After occurrence of a fault the data in the two registers are combined in a modulator for display on an oscilloscope. A complete unit typically includes several channels for simultaneous display; each channel including the apparatus described above.