Event button error & code syntax in VBA...

[BGiffin2004]

(I am using Windows XP: 32 bit version / Excel 2010)
This Function is supposed to calculate Fahrenheit from Celsius with the click of a "Calculate" button (CommandButton1). CommandButton2 is supposed to "Clear" the C & F fields – and the line is yellow highlighted for an error reason. ANY pointers would be appreciated. (See zipped picture and workbook attachments.) – Thanks!

Public Function Converter ()
C As Double, F As Double
Private Sub CommandButton1_Click ()
C13 = C ……………………………………………(C13 is the cell for the Celsius entry.)
D13 = F ……………………………………………(D13 is the cell for the Fahrenheit entry.)
F = 32 + (9 / 5) * C
End Sub
Private Sub CommandButton2_Click () …………(This line is yellow highlighted.)
Clear F, C 
End Sub
End Function