Transducers used in body support interface pressure evaluation are inconsistent and the measurement technology is poorly defined. To study the measurement and performance characteristics of interface pressure evaluating systems, calibration experiments and clinical trials were carried out with pneumatic and electropneumatic pressure transducers. The objective of the experiments was to establish the boundaries of agreement among the common pressure evaluating systems using a practical measurement protocol. Reproducible static spot, plane and curved surface calibration loads were applied to each of the transducers. Twenty normal volunteers were measured in the sitting and recumbent positions by four independent observers in two clinical laboratories. None of the transducers was found to reproduce the applied peak pressures in the calibrating modes of these experiments. When the transducers were used by skilled observers, the results showed highly significant strong correlation between the outputs of the transducers (SD < 15 mmHg) for 1,080 independent pressure measurements in the range of 20 to 100 mmHg.