Regression equations developed with data to the end of 1961 were recomputed using approximately twice the number of observations. The new equation based on data for six radiation stations using the Robitzsch actinograph is Q/QA = 0.27 + 0.50 n/N and is almost identical with the one obtained earlier. The wide spatial and temporal variation of regression equations for particular months for individual stations makes them of little value. Combining all station data for individual months produced monthly regression equations which were in close agreement with one another and with the "all-in" equation.
C.E. Hounam (Sun,) studied this question.