I have data in worksheet A for each month, for each entity. Then I have a
summary page which shows just the averages for each entity for each month.
Then I need to create a master summary page which shows just the annual
average for each entity, just one line per entity.

My Summary page shows Jan-Dec in column A. I have a formula averaging the
numbers from worksheet A. Jan-Mar is done. But the rest of the year hasn't
happened yet, so April's formula results "#DIV/0!". I have already put in
all the formulas for the year to be done with it. But I don't want all these
"#DIV/0!" to appear on the spreadsheet, it makes it look bad. I want those
cells to appear blank until there are actual numbers to be averaged, so the
formula can show a real result, not some goofy looking err-type message that
junks up the spreadsheet.