Thanks Paul,
Dmax seems to work well for finding the max record in my ID field, e.g.
ID
GEF005
GEF312
GEF807
Unbound box on form containing following Control Source code:
=Dmax("ID","MasterTable")
gives: GEF807
However, when I add +1 to the end:
=Dmax("ID",MasterTable")+1
I get #Error in...