During histogram input, the following rules are checked, and error messages are printed if the rules are violated:
The step numbers must increase monotonically, unless the -T4 command line flag is used.
The column values for the steps must increase monotonically.
The weight for each cell must be between 0.0 and 1.0.
The total of weights for a column must be close to 1.0.
The first cell represents null values and it must be present, even for columns that do not allow null values. There must be only one cell representing the null value.
Two adjacent cells cannot both use the < operator.
