Create immutable entry based on lookup

[ECTA]

I have a "Person" table that has birth date. On another table, I lookup that birthdate to find the person's current age when "Event" happened. Next year, a new "Event" will have different age for the person (as they are a year older). But I need to know what age they were at each "Event"

So how do I create a column of ages that are dynamic on entry, but don't change once they are entered?

[TheTimeSavingCo · Accepted solution]

Hmm, in the "Event" table, create a Date field called "Date of Event" or something, then create a formula field that will calculate the age by deducting the birthdate year from the "Date of Event" value year?

[ECTA]

Won't this formula update that result next year? OR are calculated fields only calculated once upon entry?

[TheTimeSavingCo]

Hm, I was thinking the formula would caclulate the difference between the date of the event and the linked person's birthday, and so there'd be no updates regardless of the current date

[ECTA]

Got it. I misunderstood. Thanks!