Set a self-relationship for that ProjectMinutes table, linked by Job Number.
Set the Meeting Number to auto-enter, set by:
Max (SelfRelationshipByJobNumber::MeetingNumber ) + 1
I created the self-relationship linked with Job number and set it to auto enter with the calculation you typed in. It doesn't seem to work since it is not auto assinging the number itself or I am doing something wrong. :)
MkII version (that handles the scenario better if you have a new record with an empty JobNumber):
JobNumber = "" ; "" ;
Max ( JobsTableSelfByJobNumber::MeetingNumber) + 1
On the MeetingNumber field, set it to auto-enter a calculation, Do Not Replace Existing Value Of Field (if any)