Step-by-step:
InfoDrainage has the capacity to accommodate standards for units and rainfall studies from around the world. You can configure the project units and rainfall theory options for your local requirements.
- In the Plan View, click any pipe.

- In the Connections dialog box, in the table headers, you can see that the units are set to metric for these pipes.

- Close the dialog.
- Click File > Preferences.

- In the Preferences dialog, click the Regionalization tab.
- Expand the Units drop-down and select United States, then close the dialog.

- Click the same pipe as before, and this time in the Connections dialog, the units are set to Imperial feet.
- Open the Preferences dialog again.
- On the Regionalization tab, click Edit.
- Expand the Region drop-down and select User Defined.

- Back in the Regionalization dialog, expand the Region drop-down and select United States.
- A warning appears, telling you that the region will be changed to Global instead.
- Close the Preferences dialog.
- On the ribbon, click the Rainfall/Pollutants.
- Review the available rainfall event types.

- On the ribbon, Preliminary Sizing tab, Network Design panel, click Network Design Criteria.

- In the Network Design Criteria dialog box, Flow Options tab, expand the Peak Flow Calculation drop-down and select Rational Method.
- Click OK.

- Open the Preferences dialog box again.
- Click Regionalization, expand the Region drop-down and select United States.
- Click the Rainfall/Pollutants tab again and review the rainfall design options now available.
