Well… It depends on what you put in the field…
Currently, Airtable does not support a ‘write once’ Formula field; that is to say, Formula fields are recalculated every time they are displayed. (The only exception to this rule exposed to the user is CREATED_TIME()
.) So the prospect of setting a ‘trigger’ with a formula along these lines —
IF({WatchedField}!=BLANK(),TODAY())
— won’t work, because Airtable determinedly lives in the present, where it’s always today…
That said, should you be fortunate enough that {WatchedField}
is a Date field, you could implement the functionality you describe — as long as you can trust the timestamp.
Alternatively, if you can design your base so that {WatchedField}
is a Linked Record field, and you can trust there to be a one-to-one correspondence between {WatchedField}
and records in the linked table (that is, each {WatchedRecord}
links to a single record in the linked table, and each record in the linked table links to no more than one {WatchedField}
, you can calculate the Δ between the main record’s CREATED_TIME()
and that of the linked record.
If you don’t need split-second accuracy — by which I mean you can live with plus or minus 20 minutes — this sounds like a perfect place to use Zapier: Define a view filtered to show records where {WatchedField}
is not empty; configure Zapier to trigger on new records being added to the view; and have Zapier respond by entering the current date and time into a timestamp Date field. Since the record to be updated is the same one that triggers the Zap, it’s considered a two-stage Zap and can be executed from a free account