A procedure for optimal selection of the measurement points to get the best calibration characteristics (for the chosen optimality criterion) of measuring apparatus is proposed. The coefficients of the calibration characteristics are evaluated by the classical least squares method. For this work, the A-optimality criterion has been used as an optimality criteria. As an example, the problem of optimal selection of the standard pressure setters (the piston gauges) during calibration of the differential pressure gage is solved. Obtained values of the optimum measurement points for the calibration of the differential pressure gage are checked via actual experiments. (C) 2010 Elsevier Ltd. All rights reserved.