HELP with Select Case script on multiple rows when cell value changes!!

Hi all, I would like to run this Select Case script which uses a number of user defined functions that are located in module1. I have used a similar script on single cell entries but now i need it to run on a number of rows/a whole Range. With the function datatype as 'Double' it doesn't run (because it needs an integer) but when i change the data type to 'Range' in each of the function's i still can't get it to run.. any idea?

Also, how do I make this script run when the value in 'B2' changes? I've found a solution for say when .Value > 0 but not for any change in value.
I'm new to vba so a helping hand would be appreciated.

Here is the file:
SampleWorkbook1.xlsm

Sub ConvRawPress()

Select Case Range("PressUnits")
        
            Case "mmHg"
                Worksheets("Output").Range("OutputPressmmHg") = Worksheets("Output").Range("RawPartialPress")
                Worksheets("Output").Range("OutputPressmBar") = Module1.mmHg2mBar(Worksheets("Output").Range("RawPartialPress"))
                Worksheets("Output").Range("OutputPresskPa") = Module1.mmHg2kPa(Range("RawPartialPress"))
            Case "mBar"
                Worksheets("Output").Range("OutputPressmBar") = Range("RawPartialPress")
                Worksheets("Output").Range("OutputPressmmHg") = Module1.mBar2mmHg(Range("RawPartialPress"))
                Worksheets("Output").Range("OutputPresskPa") = Module1.mBar2kPa(Range("RawPartialPress"))
            Case "kPa"
                Worksheets("Output").Range("OutputPresskPa") = Range("RawPartialPress")
                Worksheets("Output").Range("OutputPressmBar") = Module1.kPa2mBar(Range("RawPartialPress"))
                Worksheets("Output").Range("OutputPressmmHg") = Module1.kPa2mmHg(Range("RawPartialPress"))
    
            End Select

End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Address=Range("B2") Then
Select Case Range("PressUnits")
        
            Case "mmHg"
                Worksheets("Output").Range("OutputPressmmHg") = Worksheets("Output").Range("RawPartialPress")
                Worksheets("Output").Range("OutputPressmBar") = Module1.mmHg2mBar(Worksheets("Output").Range("RawPartialPress"))
                Worksheets("Output").Range("OutputPresskPa") = Module1.mmHg2kPa(Range("RawPartialPress"))
            Case "mBar"
                Worksheets("Output").Range("OutputPressmBar") = Range("RawPartialPress")
                Worksheets("Output").Range("OutputPressmmHg") = Module1.mBar2mmHg(Range("RawPartialPress"))
                Worksheets("Output").Range("OutputPresskPa") = Module1.mBar2kPa(Range("RawPartialPress"))
            Case "kPa"
                Worksheets("Output").Range("OutputPresskPa") = Range("RawPartialPress")
                Worksheets("Output").Range("OutputPressmBar") = Module1.kPa2mBar(Range("RawPartialPress"))
                Worksheets("Output").Range("OutputPressmmHg") = Module1.kPa2mmHg(Range("RawPartialPress"))
    
            End Select

End iF
End Sub