A method of counting frequencies, according to some classification, in a set of data. One line on a sheet of paper is assigned to each category or number, in the case of a discrete random variable, or class, in the case of grouped data. The data set is then worked through, and each item is represented by a vertical stroke on the corresponding line. For ease of counting, every fifth observation is represented by a

Tally chart. The chart is a tally of the eruption times of Old Faithful on 1 August 1978. Note the five-barred gate that makes counting the last row easy.

diagonal line crossing the previous four to make a five-barred gate. Tally charts are often used with grouped observations.