The compound period determines how often interest is compounded. It is the period (from one day to one year) after which interest is computed and added to principal. This is done for normal (compound interest) and Rule of 78 interest. Unpaid interest under U.S. Rule does not compound but is computed at each payment date and added to a special non-interest-bearing account.
The compound periods that can be selected in TValue range from Continuous to Annual.