The reference guide's step-by-step language says:

If only part of the lot is irrigated, complete the calculation twice—once for the irrigated section, and again for the unirrigated area—and sum the results.

What exactly is meant here -- do we complete 2 separate calculators (one for irrigated areas, one for non-irrigated), then a summay table of the info?  Do we use a weighted average of the percentage?  When we enter the non-irrigated area in the calculator, do we enter it as irrigated?  Can someone please clarify?  Thanks!