There are two main ways to add numbers across multiple worksheets in Excel:

1. Using the SUM Function with 3D Referencing:

This method utilizes the SUM function's ability to handle 3D references. Here's how it works:

* Identify the cells to sum: Pinpoint the cell on each worksheet that contains the value you want to add.
* Go to the cell where you want the total: Click on the cell in your summary sheet where you want the sum of all the values to be displayed.
* Enter the SUM formula: Type `=SUM(` (make sure to include the opening parenthesis).
* Select the range across worksheets: Hold down `Ctrl` on your keyboard and click on the cell containing the value in the first worksheet. Then, while still holding `Ctrl`, navigate to the last worksheet and click on the cell with the value you want to sum. This will create a range that includes all the corresponding cells across your selected worksheets.
* Close the formula: Press `Enter` to finalize the formula. Excel will automatically add the values from the specified cells on each worksheet and display the total in your chosen cell.

2. Using Consolidated Ranges:

This method involves creating a consolidated range that combines data from multiple worksheets. Here's the process:

* Prepare your data: Ensure your data on all worksheets is laid out identically in terms of row and column order.
* Go to the Data Tab: Click on the "Data" tab in the Excel ribbon.
* Consolidate Function: In the "Data Tools" group, click on the "Consolidate" function.
* Reference Range Settings: In the "Consolidate" window, choose the option under "Reference" that best describes how your data is arranged on the worksheets (e.g., "References are in first row").
* Define the range: Click the "Browse" button next to the "Consolidate area" field. Select the range containing the data you want to sum on the first worksheet.
* Include additional worksheets (Optional): If you want to include data from more worksheets, hold down `Ctrl` on your keyboard and select the corresponding ranges on the other sheets.
* Link to source data (Optional): Check the box next to "Create links to source data" if you want the consolidated range to update automatically when the source data changes.
* Click OK: Click "OK" to finalize the consolidation. Excel will create a new range containing the combined data from all specified worksheets. You can then use the SUM function on this consolidated range to get the total sum.

Choosing the Right Method:

- 3D Referencing: This method is simpler and faster for a quick sum across a few worksheets with identically positioned data.
- Consolidated Ranges: This method is better suited for complex scenarios where you might need to perform further calculations or data manipulation on the combined data set.