I have the following `VLOOKUP`

formula for a Conditional Formatting rule:

```
=VLOOKUP(A1,Sheet1!$A$2:$C$17,3,FALSE)<>0
```

This works fine and does what I want, which is this: If column C (3rd column) in the lookup table contains any value (i.e. `<>0`

), apply some formatting to the current cell.

What I don't understand is the `A1`

value used as the first argument in the formula. When I entered the above rule using `Conditional Formatting -> New rule -> Use a formula to determine which cells to format`

, I specified the entire worksheet of Sheet2. So when I enter a value in any cell in Sheet2, the formula is applied and really works beautifully.

But why does it work when the value to look up is specified as A1?

I am using Excel 2016 on Windows 7 x86.