Gravimetric and coulometry are recognized as primary method in actual measurement, so their accuracy can be appraised by their precision. The precision of measurements of ZrO2+HfO2 by mass balance of difference and gravimetric by precipitation mandelic acid was compared. It shows that the precision of mass balance of difference (0.022%) is better. There is no significant difference between the two averages. So the accuracy of mass balance of difference is higher as its precision is better.