利用方差合成规律和不确定度定义为方差的正平方根，导出拉伸试验测定的弹性模量的合成标准不确定度表示式，其可以用于评定弹性模量的合成标准不确定度。实例评定结果表明ISO 6892-1：2019附录G中式（G.4）的评定结果明显偏低，原因是式（G.4）缺失了力测量设备准确度级和延伸测量仪器准确度级所允许的误差而引起的不确定度分项。建议附录G对此进行相应的修改。

Based on the rule of variance composition and uncertainty defined as the square root of variance, the expression of composite standard uncertainty of elastic modulus measured by tensile test was derived, which can be used to evaluate the combined standard uncertainty of the elastic modulus. The evaluation results of an example show that the evaluation results of formula (G. 4) given in appendix G of ISO 6892-1:2019 was obviously lower. Because formula (G. 4) did not include the uncertainty item caused by the error allowed by the accuracy level of force measuring equipment and that of extension measuring instrument. It is suggested that appendix G should be modified accordingly.