A digital meter which displays the significant height and mean period of irregular waves on real time basis was developed. The significant wave height is calculated as 4.0η rms after computing the root-mean-square value of wave profile, ηrms' while the mean wave period is calculated by dividing the measuring time by the number of zero up crossings. A numerical simulation of irregular waves with varying durations has shown that the wave height by this method is statistically stabler than the wave height by the conventional mean wave method; the ratio of standard deviation to the mean value of ηrms is estimated to be less than 2 per cent for trains of 50 waves long.
　Tests with a newly-developed digital indicator for laboratory irregular waves have confirmed that the indicated values of heights and periods agree within an allowable error with the values directly obtained from wave profiles by the electronic digital computor.
　The present digital indicator can be easily adapted for use in the field. It can also be utilized for laboratory tests with regular waves by changing the conversion factor of 4.0 to 2.83.