Describe how the average period varies, if at all, with different string lengths, displacements and masses. Make sure any variations are significant, that is, it.s well above the noise (standard deviation). Review your results; how should the period vary according to theory? Describe how the average period varies, if at all, with different string lengths, displacements and masses. Make sure any variations are significant, that is, it.s well above the noise (standard deviation). Review your results; how should the period vary according to theory? 3. Use the period of one string length to predict the periods given other lengths. Review the result; what is the percentage error in your values?