Classes (one per line: lower, upper, frequency) 50 56.5 1 56.5 62.5 0 62.5 68.5 4 68.5 74.5 4 74.5 80.5 2 80.5 86.5 3 86.5 92.5 4 92.5 98.5 1 Lower limit, upper limit and frequency, separated by spaces or commas. A line like "10-20 5" also works. Classes must not overlap.