When creating a formula in Excel or most other spreadsheet programs we sometimes need one of the values to be dynamic (e.g. we can change it in one place and effect everywhere its referenced) but stay constant when we replicate that formula across rows or columns.
To keep a constant value in Excel use the following steps:
Step 1: Create a cell with the constant value you want to reference
Step 2: Create a formula in a cell that performs your calculation
Step 3: In the formula where you reference the value you created in step 1, add a "$" before the letter (representing the column) and number (representing the row).
For more details and explanation, check out geekbeat.tv/tip11