I’m sorry @Pepe I have to disagree with your comment.
Using the technique I described should NOT cause an issue for multiple users using the app at the same time. This is what the AppSheet platform is designed for.
It is true, that the SAME single row in the table will be updated multiple times by different users with different values. But this single row is simply a place-holder and although it may be updated by multiple users with differing values AND potentially that updated row could be pulled down to another users device with a Sync, if the Column definitions are updated correctly with Initial Values and “Reset on Edit” flags set, Users will NEVER see those other values entered by other users.
However, if you have any data privacy concerns at all, you can add a placeholder row for each user (i.e. add an Email column in the table to identify the user specific row by their login email). The “Row Key” property in the Form view can use an expression to identify the correct row key. You would need to get creative to ADD the user specific placeholder rows - either add the row manually when you add a new user to the app OR you can create a Group action to launch the “calculator” Form. It would check first if there is a row in the table, add one if not and then launch the Form.