Identify the class limits for each class interval
Subtract 0.5 from each lower class limit to get the lower class boundary
Add 0.5 to each upper class limit to get the upper class boundary
Use the same adjustment for all classes when data are measured to the nearest whole number
For data measured to one decimal place, subtract and add 0.05 instead of 0.5
For data measured to two decimal places, subtract and add 0.005 instead of 0.5
Ensure adjacent class boundaries do not overlap
Check that the boundaries cover all values in the data set