Calculation formula help

I am brand new to using Adobe forms and formulas. I have a column that will calculate a "project completed percentage" based on the "scheduled value" and "total completed" for each row. I need this form to be empty to pass on to others to fill out but when I have the "scheduled value" column empty there are all these errors that pop up for each row in the "completed percentage" column. How can I prevent the error pop up for each row when that row's schedule value is empty?