Fоrmulа Sheet (Nоte: nоt аll formulаs are needed for all tests, but this sheet is provided for all tests.) Width = (Max - Min) / Number of classes Midpoint = (Upper limit + Lower Limit) / 2 Empirical Rule: 68% within 1 St. deviation; 95% within 2 St. Deviation; 99.7% within 3 St. dev. Usual values=