When first starting out in FileMaker things like Auto Entry compared to lookup fields or even regular calculations can be confusing. Auto Entry Calculations can use foreign or child fields from another table or file, though you will find that when data changes the Auto - Calculation will not automatically update. The reason for this is that the Auto Entry Calculation is designed to update when a field in the calculation from the same table is modified. Lookup Fields are designed to capture the data and store it until the relationship is refreshed. The Advantage of an Auto Entry Calculation over a Lookup in reference to a relationship is that you can conditionally dictate the result in the "Lookup" like behavior. If you are using an Auto Entry Calculation and referencing a child field from another table or file, you can refresh the data if you refresh the relationship be set fielding the key on the parent side with itself.

Recap:

Lookup Fields:

- Use a lookup field when you want to capture data that will not change unless the relationship is refreshed.

Auto Entry Calculation:

- Use when you want to update content based on another parent table field in the same table but allow the result to be modifiable.

- Use when you want to lookup data from another table or file but need to conditionally set which field or data. This will act like a lookup but will give you the added advantage of several options of data based on your calculation. Note like a lookup the data can refresh in this scenario if you refresh the relationship.