Abstract: An automatic liquid sampler for a gas chromatograph includes a sampling mechanism and a control system which controls both the sampling mechanism and other functions of the chromatograph. Four sub-programs are stored in an integrated circuit read-only memory. A complete program for analyzing a series of samples consists of a sequence of the sub-programs read out by a counter under the control of a logic switch unit connected between the final stages of the counter and the most significant address inputs of the memory. The logic switch unit includes a rotary wafer switch which can be manually set to one of twelve positions each corresponding to a unique complete program made up from the sub-programs according to the wiring of the switch.