A histogram made by counting events can be regarded as a measurement of a probability distribution. Allowing for statistical error, the height of each bin represents the probability of an event where the value of @math{x} falls in the range of that bin. The probability distribution function has the one-dimensional form @math{p(x)dx} where,
In this equation @math{n_i} is the number of events in the bin which contains @math{x}, @math{w_i} is the width of the bin and @math{N} is the total number of events. The distribution of events within each bin is assumed to be uniform.