Android Question CallSub warning #25

Sub Globals
    Dim ZLetter As String
End Sub

Sub GPS_LocationChanged (Location1 As Location)
    CallSub(ZoneLetter,"ZLetter")
    lblZone.Text = "Zone = " & Zone & ZLetter
End Sub

Sub ZoneLetter
      If((84 >= Latx) AND (Latx >= 72)) Then 
        ZLetter = "X"
    Else If((72 > Latx) AND (Latx >= 64)) Then
        ZLetter = "W"
    Else If((64 > Latx) AND (Latx >= 56)) Then
        ZLetter = "V"
    Else If((56 > Latx) AND (Latx >= 48)) Then
        ZLetter = "U"
    Else If((48 > Latx) AND (Latx >= 40)) Then
        ZLetter = "T"
    Else If((40 > Latx) AND (Latx >= 32)) Then
        ZLetter = "S"
    Else If((32 > Latx) AND (Latx >= 24)) Then
        ZLetter = "R"
    Else If((24 > Latx) AND (Latx >= 16)) Then
        ZLetter = "Q"
    Else If((16 > Latx) AND (Latx >= 8)) Then
        ZLetter = "P"
    Else If(( 8 > Latx) AND (Latx >= 0)) Then
        ZLetter = "N"
    Else If(( 0 > Latx) AND (Latx >= -8)) Then
        ZLetter = "M"
    Else If((-8> Latx) AND (Latx >= -16)) Then
        ZLetter = "L"
    Else If((-16 > Latx) AND (Latx >= -24)) Then
        ZLetter = "K"
    Else If((-24 > Latx) AND (Latx >= -32)) Then
        ZLetter = "J"
    Else If((-32 > Latx) AND (Latx >= -40)) Then
        ZLetter = "H"
    Else If((-40 > Latx) AND (Latx >= -48)) Then
        ZLetter = "G"
    Else If((-48 > Latx) AND (Latx >= -56)) Then
        ZLetter = "F"
    Else If((-56 > Latx) AND (Latx >= -64)) Then
        ZLetter = "E"
    Else If((-64 > Latx) AND (Latx >= -72)) Then
        ZLetter = "D"
    Else If((-72 > Latx) AND (Latx >= -80)) Then
        ZLetter = "C"
    Else
        ZLetter = "Z" 
    End If
   
End Sub