Declaring ActiveChart Object

Hello,

the chart is active because the code just created it.

What is the question?

The active chart is a chart object. The parent of a chart object is the chart object collection. The parent of that is the sheet.

If you want to create a new chart:

Sub AddChartObject()
Dim myChtObj As ChartObject
'
    Set myChtObj = ActiveSheet.ChartObjects.Add _
        (Left:=100, Width:=375, Top:=75, Height:=225)
    myChtObj.Chart.SetSourceData Source:=Sheets("Sheet1").Range("A3:G14")
    myChtObj.Chart.ChartType = xlXYScatterLines
End Sub

If you want to manipulate an existing chart

Sub SetChartAxisScale()
Dim ws As Worksheet
Dim myChtObj As ChartObject
    Set ws = ThisWorkbook.Worksheets("ITF_Chart")
    Set myChtObj = ws.ChartObjects("Chart 3")
    With myChtObj.Chart.Axes(xlValue)
        .MaximumScale = 44
    End With
End Sub

To avoid names you can select and/or set charts with a value based on creation.
1 if it is the first and only chart on the sheet. If you are manipulating the 3rd chart then put 3...
ws.ChartObjects(1) instead of ws.ChartObjects("Chart 3") helps to know when creating loops on charts - not sure you really need it in this case but something to note -

Cheers