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Toggle absolute and relative references

Windows shortcut 
F4
Mac shortcut 
T

While editing a formula, this shortcut toggles cell references from relative to absolute, to partially absolute, back to relative again:

A1 --> $A$1 --> A$1-- > $A1-- > A1

It's much faster and easier than typing $ characters manually.

To convert an existing formula, enter cell edit mode, place the cursor in or next to the reference you'd like to convert, then use the shortcut.

Note: in Excel 2016 for the Mac, you can also use fn + F4. 

Related videos

The videos below demonstrate this shortcut.
In this video, we'll look at how to create a dynamic named range using the OFFSET function, the most common way to create dynamic names range with a formula.
This video shows how to use VLOOKUP to merge data in two tables based on a common ID. You can even use this technique to reorder the columns you retrieve.
In this video, we'll look at how to use the HLOOKUP function. HLOOKUP works like VLOOKUP, but is meant for data in a horizontal arrangement.
In this video, we'll look at how to create a bar chart in Excel to show survey data. Bar charts are good for long labels, since there is plenty of room for text to the left of the bars. 
In this video, we look at how to create a mixed reference that is part relative, and part absolute, useful when you want only part of a cell reference to change.