I suspect you did not design that workbook, otherwise there would be no such mystery.
IF works like this: IF(Condition,Result when true, Result when false)
.
=IF(PlotChoice="GAS",1,2)
If the range name "PlotChoice" equals "Gas", then return 1, else return 2. The result is one of two possible values. If you need to select between three, then you need to nest the IF Statements.
=IF(PlotChoice="GAS",1,IF(PlotChoice="Maintenance",2, 3))
If the range name "PlotChoice" equals "Gas", then return 1, else there is another IF(). If the range name "PlotChoice" equals "Maintenance" then return 2, else return 3.
You can continue this kind of nesting for more levels than is advisable. For scenarios with more than three or four possible outcomes there are more efficient and maintainable options.