60. Now let’s go to cell F4 again.
61. Edit the formula and change it to =IF(E4=””,””,E4-$B4) and press Enter.
62. The only thing you are change is placing a $ sign in front of the reference to cell B4. This change is to place an absolute reference to column B. When you copy or fill this cell, the reference will always stay with column B, but change the rest of the formula.
63. Now click on cell F4 and press CTRL+C to copy the formula. Paste it in cell H4. View the formula in cell H4: 
64. The “B” part stayed the same, while the rest of the formula changed to reflect its new location.
65. Now, fill the formula down in the column to all of the empty cells.
66. Now repeat the process of copying the formula over to the rest of the “Difference” columns for the other months until all of them have the formula filled in.
67. Remember to go back to January and all of February and change the formula to match the new one.
