An ISO/TC 164/SC 1 working group has developed procedures for determining the measurement uncertainty of force-proving instruments. These procedures have been added to this standard as a new annex (Annex C). In addition, this standard allows the calibration to be performed in two ways: - with reversible measurement for force-proving instruments which are going to be used with increasing and decreasing forces; - without reversible measurement for force-proving instruments which are going to be used only with increasing forces. In the first case, that is, when the force-proving instrument is going to be used for reversible measurements, the calibration has to be performed with increasing and decreasing forces to determine the hysteresis of the force-proving instrument. In this case, there is no need to perform a creep test. In the second case, that is, when the force-proving instrument is not going to be used for reversible measurements, the calibration is performed with increasing forces only but, in addition, a creep test has to be performed. In this case, there is no need to determine the hysteresis. This International Standard specifies a method for the calibration of force-proving instruments used for the static verification of uniaxial testing machines (for example, tension/compression testing machines) and describes a procedure for the classification of these instruments. This International Standard is generally applicable to force-proving instruments in which the force is determined by measuring the elastic deformation of a loaded member or a quantity which is proportional to it. This document (EN ISO 376:2011) has been prepared by Technical Committee ISO/TC 164/SC 1 "Unaxial testing" (secretariat: AFNOR, France) with intensive German collaboration and shall be adopted as European Standard within the framework of a parallel voting procedure. Regarding the German collaboration, the responsible Working Committee is NA 062-08-11 AA "Werkstoffprüfmaschinen" of the Materials Testing Standards Committee (NMP).