Pass A Variable To The Form Code

I have a spreadsheet with about 30 charts on it that I would like to attach a macro to which opens the chart in a form. I've figured out how to do this last part, but am stuck on how to pass a variable to the form code which tells excel which chart to copy. Essentially what I'm doing creating a macro for each chart which would run when that chart is clicked on. This macro is identical for each chart except for the name of the chart being passed.

Sub Chart1_click()
ShowChart "Chart 1"
End Sub

Sub ShowChart(c As String)
frmChart.Show
End Sub

In the UserForm_Initialize code located in the userform module, I'd like to call the code which saves and loads the image of the clicked on chart. But here's where I'm stuck. How do I pass c to the code in the form module...e.g, how to pass c to UserForm_Intialize and to ChartZoom? Here's what I have so far...

Private Sub UserForm_Initialize(c As String)
ChartZoom c
End Sub

Private Sub ChartZoom(c As String)

frmChart.Show

Dim Cht As Chart
Set Cht = ActiveSheet.ChartObjects(c).chart
Dim CName As String
CName = ThisWorkbook.Path & "cht.gif"
Cht.Export Filename:=CName, FilterName:="GIF"
imgCht.PictureSizeMode = fmPictureSizeModeZoom
imgCht.Picture = LoadPicture(CName)

End Sub