Recordset not updateable

[stepone]

Hi I have two tables - one which holds call data for telephone calls, the other of which is a lookup with dialling code information. I want to link the first 5 digits of the dialled number with the area code in the lookup table.

Fine so far - but the resulting recordset is not updateable. Is this because I am linking using a calculated field = Left([dialledNumber], 5) ?

Is there a way around this ?

Thanks,
StepOne