Values people can overwrite
A calculated field is a real input. The calculation fills it in so there is less to type, and the person can type over the top when the situation on the ground is not what the form assumed.
If a value must not be edited — a total, something rolled up from a subform — mark the field read-only. Then the calculation owns it outright and nobody can change it.
The rule, in one line. Read-only is the switch. Off, the calculation seeds the field and the person has the last word. On, the calculation has the last word. There is no second mechanism.
Two details worth knowing
Clearing a field counts as typing in it. If somebody empties a calculated field on purpose, it stays empty; the calculation does not refill it.
A draft you come back to is left alone. Once a form is reopened there is no way to tell a saved calculation from a saved override, so the app does not guess. The calculation runs again only when one of its inputs changes.
Which to choose
| The value is… | Read-only |
|---|---|
| a total or a rollup that must be right | on |
| a default that is usually right but sometimes not | off |
| an estimate the person should confirm or correct | off |
| shown for information and never stored | consider a Label field instead |