Het veld is bedoeld om berekeningen te maken op tabelniveau. Als je dit type kiest, kun je een expressie maken op basis van andere velden in de tabel.
Allen Browne zegt er dit van...
What about Calculated fields in Access 2010?
Access 2010 allows you to put a calculated field into a table, like this:
Just choose Calculated in the data type, and Expression appears below it. Type the expression. Access will then calculate it each time you enter your record.
This may seem simple, but it creates more problems that it solves. You will quickly find that the expressions are limited. You will also find it makes your database useless for anyone who needs to use it in Access 2007. Instead of reading the data, they will get a message like this:
Even more serious, the calculated results are not reliable. If you change the Expression after data has been entered into the table, the existing results may not be updated correctly (through new records are edits are updated), so you cannot rely on the results. A compact/repair does not recalculate, so there is no obvious way to repair the bad results.
Since you cannot index calculated fields anyway, there is no performance benefit to be gained from using them. You are violating fundamental rules of data normalization for no good purpose. We recommend you use queries for calculated fields, just as in previous versions.
De conclusie lijkt mij duidelijk
