The Probability Box is used to determine the mean, true range, strength, square and standard deviation of range and volume for a selected number of bars. The volume values are only available for data files that contain volume data. You can extend the Probability Box in any direction (forwards or backwards). The top and bottom of the Probability Box is always set to the closing values of the first and last bars selected.
This is a companion discussion topic for the original entry at https://www.optuma.com/kb/optuma/tools/statistical/probability-box