The SUM function combined with IFERROR is a powerful way to handle errors and ensure accurate calculations in Excel. Here's how it works:

SUM Function:

The SUM function adds up a range of numerical values. For example, `=SUM(A1:A10)` would add the values in cells A1 through A10.

IFERROR Function:

The IFERROR function checks for an error in a specified cell or range. If it encounters an error, it returns a user-defined value (typically 0) instead of displaying the error itself. Otherwise, it returns the original value from the cell.

Combining SUM and IFERROR:

By nesting IFERROR within the SUM function, you can tell Excel to:

1. Evaluate each cell in the specified range.
2. If there's an error: Replace the error with a defined value (usually 0).
3. If there's no error: Keep the original value.
4. Finally, SUM all the values (including the replaced zeros for errors) to get the total.

Here are two ways to achieve this:

Method 1: Array Formula (Ctrl+Shift+Enter)

```excel
=SUM(IFERROR(A1:A10,0))
```

In this formula:

- `A1:A10` is the range of cells you want to sum.
- `0` is the value used to replace errors (you can change this to another value if needed).

Press Ctrl+Shift+Enter instead of just Enter to create an array formula. This is crucial because the IFERROR function needs to be applied to each cell in the range simultaneously.

Method 2: Standard Formula (For Excel 365 and similar versions)

```excel
=SUM(AGGREGATE(SUM,1,A1:A10))
```

This formula uses the AGGREGATE function, which has an option to ignore errors. Here:

- `SUM` specifies the operation (summation).
- `1` indicates to ignore errors.
- `A1:A10` is the range to sum.

Both methods achieve the same result: they calculate the sum of the range A1:A10 while ignoring any errors present in those cells.

Benefits of Using SUM with IFERROR:

- Clean and Accurate Results: Prevents errors from skewing your calculations and ensures a reliable total.
- Flexibility: You can replace "0" with another value depending on your needs (e.g., replace errors with the average value).

Remember: While IFERROR helps manage errors, it's still important to investigate the source of the errors in your data for better data quality.