1. Experimental differences in errors of piston systems with normal cylinders coincide with those calculated from M. K. Zhokhovskii's formulas up to pressures of 10,000 kg-wt/cm2. The discrepancies between the experimental and calculated results do not exceed 0.05% at maximum pressure and are due to a distortion of the regular initial shape of the piston and probably of the cylinder bore. 2. For piston systems with counter-pressure and a range extending up to 10,000 kg-wt/cm2 whose pistons are fitted to the cylinders by means of the existing method, the propositions made in paragraph 1 will apply up to pressures of the order of 5,000–6,000 kg-wt/cm2. At higher pressures the effect of the “closing” of the clearance begins to disturb the normal operating conditions of piston systems and produces a discrepancy between the theoretical and experimental values of the corrections. The application of the calculated corrections in the above systems with the existing setting of the clearance becomes permissible up to 10,000 kg-wt/cm2 providing the clearance between the piston and cylinder is increased in the upper part of the cylinder. 3. For a better than a 0.05% agreement between the theoretical and experimental values of error deformations, additional investigation concerning the regular shape of the piston and cylinder bore is required.