Access 2010 VBA Case Select Function

Hi Experts,

I tried to create a function which utilizes a number scale to convert a value to a mapped number as follows:

Function IGMap()
Dim IG As Double
Dim Map As Double
 
     Select Case IG
        Case Is < 16
            Map = 15
        Case Is >= 16 And IG < 18
            Map = 17
        Case Is >= 18 And IG < 20
            Map = 19
        Case Is >= 20 And IG < 21.5
            Map = 21
        Case Is >= 21.5 And IG < 23.5
            Map = 22
        Case Is >= 23.5 And IG < 26
            Map = 25
        Case Is >= 26 And IG < 28.5
            Map = 27
        Case Is >= 28.5 And IG < 35
            Map = 30
        Case Is >= 33 And IG < 50
            Map = 40
        Case Is >= 50 And IG < 62.5
            Map = 60
        Case Is >= 62.5 And IG < 67.5
            Map = 65
        Case Is >= 67.5 And IG < 71.5
            Map = 70
        Case Is >= 71.5 And IG < 74
            Map = 73
        Case Is >= 73 And IG < 76
            Map = 75
        Case Is >= 76 And IG < 78.5
            Map = 77
        Case Is >= 78.5 And IG < 81.5
            Map = 80
        Case Is >= 81.5 And IG < 84
            Map = 83
        Case Is >= 84 And IG < 86
            Map = 85
        Case Is >= 86 And IG < 88.5
            Map = 87
        Case Is >= 88.5 And IG < 92.5
            Map = 90
        Case Is >= 92.5 And IG < 96.5
            Map = 95
        Case Is >= 96.5 And IG < 98.5
            Map = 98
        Case Else
            Map = 99
        End Select
    IGMap = Map

End Function

When I use IGMap() in the criteria of a query, the query will run, but will return no values.  If I try instead to input a field value such as:  Test:  IGMap([field]) I get the error message 'The expression you entered has a function containing the wrong number of arguments.'

Any help on what I am doing wrong would be appreciated.

Thanks!