An unusual combination of a laboratory experiment and in situ measurement of pressure fluctuations during an earthquake allows us to resolve some uncertainties in bottom pressure recorders (BPRs). In situ BPRs are usually contaminated by seismic waves during earthquakes; thus uncertainty still remains in the data obtained from BPRs. We examine in situ BPR data together with pressure variations produced by a dead weight (a pressure standard) in a laboratory experiment during an earthquake. The features recorded by the in situ BPRs are analysed as part of the overall experiment. We demonstrated that a 10-kg dead weight on a piston-cylinder across an area of 10 mm(2) is capable of reproducing pressure fluctuations at a depth of 1000 m in the water column. The experiment also indicates that the internal mechanics of BPRs are isolated from incident seismic waves, suggesting that BPRs measure true in situ pressures without instrumentally induced disturbances. This constitutes the first instance in which pressure fluctuations recorded by in situ BPRs during an earthquake were reproduced using a pressure standard in the laboratory.