Excel Extend series - all rows

I recently had to deal with very large (300K+ rows) Excel spreadsheets. I needed to add an additional column based on calculations of other existing columns. I was familiar with the extend series functionality of Excel for extrapolating a function over multiple rows, but what a pain to drag for 300,000 rows. There has to be an easier way to apply a function to all rows. So I Googled and found a nice easy way to Extend Series to all rows, just double-click the square in the bottom right corner of the column with the function applied and presto, the calculation is applied to all rows in the spreadsheet:

Create the function in row 1


You can extend the function to subsequent rows by dragging the square in the bottom right corner of the selected cell...


...or just double-click the black square, and the function is extended all the way to the last cell ie; the 17th row function is =a17*b17.


Special thanks to Phil for his help.