[API: VBA] SetRealValue

Hi all,

I'm still learning how to use API for Mathcad and I have a few questions about this function, SetRealValue.

1) why doesn't the code below work? I mean there are obviously no error, but it doesn't do what I want. In the selected worksheet has x:=2, I was trying to get this x:=2 to be x:=3m. This code below doesn't change anything in this sheet.

Sub test01()

 Dim WS As Ptc_MathcadPrime_Automation.Worksheet
 Dim App As Ptc_MathcadPrime_Automation.Application
 Dim FileName
 Set App = New Ptc_MathcadPrime_Automation.Application
 FileName = Application.GetOpenFilename(MultiSelect:=False)
 Set WS = App.Open(FileName)
 Call WS.SetRealValue(x, 3, "m")
 
End Sub

2), why are there so many functions with the same name reappear in a few different classes? are they doing the same thing? If not, what are the differences? For examples, this SetRealValue occurs in three differences classes: IMathcadPrimeWorksheet, IMathcadPrimeWorksheet2, and Worksheet.

3) The input format for this function is variable name as string, value as double, and unit as string. What if I want to assign string as the value, can I still use this function as just assign string? or there are other functions for that?

Add 4). What happens if I have a variable defined multiple times throughout the sheet? Let say I have x:=.... in page 1 and x:=... in page2 and x:=... in page10. Which one of these will be changed? Is there a way to specify which of these x:= I want to change? 

For example:

Page1
x:= 1

y:= x+1 = 2

Page2

x:= 2

y:= x+1 = 3

Page10

x:= 5

y:= x+1 = 6

which of these xs will be affected by this SetRealValue?

Thank you very much!