It’s important in engineering to document your work and show how you got a result. One of the complaints engineers often have about Excel is that it’s difficult to understand the equations that are being used. One way to document references and equations is to use comments.
It’s easy to add comments to any cell. Right-click the cell and select Insert Comment. A box will appear that you can add text or equations to:

For example, you can enter the equation to calculate static deflection. When someone else opens the spreadsheet, they’ll know that the cell contains a comment because there will be a red triangle in the upper right corner. If they hover over the cell, the comment will be displayed
If you need to make your comments visible all the time, you can right-click on the cell and choose Show/Hide Comments:
You can hide it again later by right-clicking and choosing Hide Comment. You can also easily edit or delete the comment by right-clicking.
At times, it may be necessary to document a reference on your spreadsheet. Comments work well for this too. If you have a web address that you’d like to link to in a comment, Excel will turn it into a clickable hyperlink. Copy the URL from your web browser (Ctrl-C), then right-click on the relevant cell in Excel. Select Insert Comment and paste the URL with Ctrl-V.
The only downside to this that you can’t click the link unless you set the comment to “Show” because when you move the mouse to click on the link, you’re no longer hovering over the commented cell, and the comment disappears. Simply right-click on the cell and choose Show/Hide Comments, and you’ll be able to click on that reference.