Conditional Function Help

Hi, I have a spreadsheet which occasionally has cells with empty data. The spreadsheet is downloaded daily from an online table so I don't always know where the empty cells are placed (see column A in attached example). I need to write a formula to calculate return data in column B. So far, the best I have is =IF(AND(A3<>"",A2<>""),A3/A2-1,"") but this does not generate the desired result.

I need help with the first part of the formula. For example, if cell A4 has data but A3 does not have data, I then want the formula to use A2 to calculate returns. For example, (A4/A2-1,""). If A3 has data, then the formula should read (A4/A3-1,"")