To discover whether a protocol for calibration can improve the accuracy of intraocular pressure measuerements.A protocol for checking the calibration of equipment was implemented in an ophthalmic outpatient department. After seven months, calibration checks were compared with those done on equipment in other ophthalmic areas that were not following a protocol.There was a statistically significant association between errors and areas not following the protocol (p = 0.02). In comparing errors found in the area using the protocol with all other areas, a significant difference was evident at the test point of 20 mmHg (p = 0.003).Using a protocol significantly reduces calibration errors.