Try something like this Function
Function CollIdValue(strPrefix As String)
Select Case Asc(UCase(Left(strPrefix, 1)))
Case Is < 70 'A,B,C,D,E
CollIdValue = "1"
Case Is = 70 'F
Select Case Asc(UCase(Right(strPrefix, 1)))
Case Is < 71 'G
CollIdValue = "1"
Case Else
CollIdValue = "2"
End Select
Case 71 To 75 'G,H,I,J,K
CollIdValue = "2"
Case 76 'L
Select Case Asc(UCase(Right(strPrefix, 1)))
Case Is < 77 'M
CollIdValue = "2"
Case Else
CollIdValue = "3"
End Select
Case 77 To 81 'M,N,O,P,Q
CollIdValue = "3"
Case 82 'R
Select Case Asc(UCase(Right(strPrefix, 1)))
Case Is < 83 'S
CollIdValue = "3"
Case Else
CollIdValue = "4"
End Select
Case Else
CollIdValue = "4"
End Select
End Function
Then just pass the Prefix field to the Function
CollID = CollIdValue([Prefix])
PaulF