All computations in XPRafts are carried out in discrete time increments sequentially working from time zero through a rainfall event. The time increment is designated the routing increment and is expressed in decimal minutes. There are no absolute limits to its magnitude.

The selected routing increment should be the minimum needed to span enough of the expected runoff hydrograph to obtain the required information. In many instances this may not require the whole hydrograph to be developed. In some instances however, such as loss rate calibration, the full hydrograph recession may be required.

The current workbench software is limited to 2000 routing increments in any one pass. An additional requirement is that a routing increment should be wholly divisible into a partition of a rainfall temporal pattern to prevent the loss of a fraction of a rainfall in each increment. If this is neglected an appropriate warning message is generated. Additionally the routing increment should be no longer than the shortest link lag time.