On the basis of the experiments of basic measurement and diffraction grating,the error of equal precision measurement and unequal precision measurement is respectively analysed,and the methods of data processing are set forth.

As there exist some problems about measuring surface tension coefficient of liquid in the experiment in college textbook "General Physics Experiment",the authors have made serious analysis and found out that some physical quantities are not unanimous and not identical accuracy measurement before and after the traditional experiment.

Theoretical reseache on the optimum estimated value and the standard errors in the equiprecision measurement;

It is deduced by probability theory that the optical estimated value in equiprecision measurement is arithmetic average,and the formula of standard error is deduced as well.

To complete the surface tests of 3D profile with CMM,based on tip compensation,the equiangular gradu- ated measurement and equidistance graduated measurement are suggested.