UserDefCounter

Dim db as DataBase
Dim rs As RecordSet
Dim t%
Dim SQL$
Const tbnaam$ = [yourtablename]
Const DBNaam$ = [yourdatabasename]

Set db = OpenDatabase(DBNaam)
t% = 1
SQL$ = "SELECT * FROM " & tbnaam & " ORDER BY number"
Set rs = db.OpenRecordset(SQL$)
Do While Not rs.EOF
If rs.Fields(0).Value <> t% Then
'show number that's missing and do what you want

MsgBox Str(rs.Fields(0).Value + 1)
Exit Do
End If
rs.MoveNext
t% = t% + 1
Loop

'no number-gap so use t% as new counternumber


'You see.. it's possible but when your database is getting very large

'then it will cost some time to search for a number-gap.