We have a last-modified column in one of our sheets. We use it to detect when rows in the sheet have been last modified, driving discussions about the updates.
In this sheet, another column displays a "project completion date," which is just a manually entered date indicating the project owner's best guess as to when the project will be complete. (I guess that's more detail than necessary for this discussion. It's just a date, for this discussion.)
Because date math is hard for humans to do, we recently added another column, next to the completion date, which indicates the number of weeks until that date. This is an automatically generated value, based on the date. Essentially, it's "=(TheDateCell - today()) / 7". It works great, and it makes it super easy for our readers to visualize what the corresponding date really means, relative to other dates.
The only problem is, because our formula makes use of "today()", every time the sheet is opened, the last-modified column for the row updates to today as well! This makes it impossible to continue using that column to track changes.
Is there a way to display the last-modified date of a row while excluding "pseudo-updates" that are formula-based (which, arguably, aren't really updates)?