Spreadsheets have very rich and expressive formula capabilities. These are well-documented by the spreadsheet providers like Excel and Google Sheets. When the mobile app reads data from the spreadsheet, the formula values are computed. Likewise, when data is updated and synced back to the spreadsheet, the appropriate formulas are computed again.
There are two kinds of spreadsheet formulas:
In-row formulas: these are formulas that only use values from other cells in the same row. For example, if the formula for cell C2 = A2 + B2
Multi-row formulas: these are formulas that use values from cells in other rows. For example, if the formula for cell C2 = C1 + 1
Columns with spreadsheet formulas are treated as Read-Only by AppSheet. This is because spreadsheet formulas cannot be evaluated in the mobile app. However, they are evaluated when data is sent to or from the backend spreadsheet.
If all the cells in a column have the same formula, AppSheet recognizes that the intent is for all new rows to also have that formula. As a result, new rows inserted will include the formula.
On the other hand, if some cells in a column have a formula and other cells have either no formula or a different formula, AppSheet will issue a warning to the app creator. The column will be marked Read-Only but new rows will not be assigned a formula in this column (because it is not clear what the desired intent is).
For more information regarding mismatched spreadsheet formulas see this article.
Multi-row formulas with aggregates
A common use of multi-row formulas in a spreadsheet is to compute aggregate functions (totals, averages, etc). For example, a spreadsheet with individual order items followed by a row with the order total. AppSheet apps require that the rows in the same table be all of a similar nature --- i.e. all order items --- because clearly there are different app behaviors expected with order items and order totals.
AppSheet ignores rows with aggregate multi-row formulas after issuing a warning to the app creator. This applies to both "totals rows" and "sub-totals" rows.
Note: spreadsheet formulas are distinct from App Formulas. The two mechanisms are complementary and both add value to your app. App Formulas run while the user is updating data in the app, and will work even when the app is offline.