For simplicity, we use the term "Legacy Excel" to refer to any version of Excel before *before* dynamic array formulas were introduced. Practically speaking, this means Excel 2019 and older, since Excel 365 and Excel 2021 are the *only* versions of Excel that include dynamic array formulas and new functions like SORT, UNIQUE, FILTER, SEQUENCE, and XLOOKUP.

Dynamic array formulas are a huge change to the Excel formula engine because they let you easily work with multiple values at the same time in a formula. In practical terms, this means array formulas "just work". In Legacy Excel, most array formulas still need to be entered with control + shift + enter.

### Example

The LEN function returns the length of a text string as a number:

```
=LEN("apple") // returns 5
```

To get a total of all characters in a range, you can wrap LEN inside the SUM function like this:

```
=SUM(LEN(range)) // total characters in range
```

This is a simple array formula, but it must be entered with control + shift + enter in Legacy Excel:

```
{=SUM(LEN(B5:B10))}
```

*Note: Excel will add the curly brackets automatically when the formula is entered with control + shift + enter. Do not add the curly braces manually.*

In Modern Excel, the same formula below will work as-is, without special handling:

```
=SUM(LEN(B5:B10))
```

The bottom line is that array formulas in Legacy Excel need special handling. In current versions of Excel, array formulas just work.