### Catchment Opening Area

This is the area of the catchment opening. It is used to calculate the
precipitation rate. If the opening is round then use the formula:

π (d/2)^{2}

Where d = the diameter of the opening in inches.

If you are using container that is square with rounded corners such as a
plastic storage container then trace on a piece of graph paper and count the
enclosed squares to determine the number of square inches.