Function Interp(a As Range, Arng As Range, Krng As Range) As Single
Dim al, ks, i As Integer, i1_n As Integer, i2_n As Integer
Dim Arng1() As Single, Krng1() As Single
Dim cel As Range
For Each cel In Arng
If cel <> "" Then
    i1_n = i1_n + 1
    ReDim Preserve Arng1(i1_n)
    Arng1(i1_n) = cel
End If
Next cel
For Each cel In Krng
If cel <> "" Then
    i2_n = i2_n + 1
    ReDim Preserve Krng1(i2_n)
    Krng1(i2_n) = cel
End If
Next cel
Do
    i = i + 1
Loop While Arng1(i) < a.Value
'If i = 1 Then Exit Function
If Arng1(i) = a.Value Then
    Interp = Krng1(i)
Else
    Interp = (Krng1(i) - Krng1(i - 1)) / (Arng1(i) - Arng1(i - 1)) * _
            (a.Value - Arng1(i - 1)) + Krng1(i - 1)
End If
End Function