a method of operating liquid chromatography apparatus . the method includes the steps of determining a given rate of liquid flow desired from a piston pump to the column ; establishing for the piston a predetermined stroke length and rate of reciprocation for providing the given rate of liquid flow ; determining for each cycle of the pump a desired liquid volume that would be delivered to the column by the pump if producing the given rate of liquid flow ; ascertaining for each cycle of the pump the actual liquid volume delivered thereby to the column ; determining for a predetermined operating period of the pump the total desired liquid volume that would have been delivered to the column by the pump if producing the given rate of liquid flow during each cycle of the predetermined operating period ; and determining the total actual liquid volume delivered to said column by said pump during all cycles of said predetermined operating period . after comparing the total desired liquid volume with the total actual liquid volume one or more subsequent piston cycles are produced that provide a compensating liquid flow rate different than the given rate of liquid flow in response to a determination during the comparing step that a difference exists between the total actual liquid volume and the total desired liquid volume . the compensating rates of liquid flow correct pumping cycle errors that produce incorrect liquid volume flow .