Right now, there is no easy way to get individual fields to re-calculate. It’s pretty much all (every field on the sheet) or nothing. Individual field re-calculation requires scripting that is beyond the ability or comfort zone of most users, and Ragic! support apparently can’t/won’t help either.
Seems to me it would be much easier for users if every calculation field in the design layout had a checkbox (or similar) that could toggle re-calculation on/off, possibly along with a time field indicating when the field is to be re-calculated. (daily, weekly, monthly, etc.)