A number of independent readings of “typical” seismographic records are made, primarily in order to estimate the errors involved in determining the onset of a P wave. The degree of consistency with which a disturbance is called “the first arrival from an earthquake” is discussed. The distribution of reading errors is estimated and a method suggested for improving the accuracy of routine reading of seismograms. This model provides estimates for reading errors of several types of onsets. Finally the classification of onsets into “i” and “e” is shown to be inadequately defined.

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