The main difference between A1-style and R1C1-style references in the ADDRESS function is how the row and column numbers are represented. In A1-style references, the row number is represented by a number, and the column number is represented by the column letter. For example, the cell address A1 refers to the cell in the first row and column. In R1C1-style references, both the row and column numbers are represented by numbers. For example, the cell address R1C1 refers to the cell in the first row and column. The default reference style in Excel is A1-style. However, you can change the reference style to R1C1 by going to File > Options > Formulas and selecting the R1C1 reference style check box. The ADDRESS function can return either A1-style or R1C1-style references, depending on the value of the reference_style argument. If the reference_style argument is omitted or set to 4, the function will return an A1-style reference. If the reference_style argument is set to 5, the function will return an R1C1-style reference.