Why does my trendline equation change?

I've got a somewhat complicated XY Scatter chart. When I view one data series, the linear trendline equation is 'y=-30.179x+5427.5'. When I add a 2nd data series, it changes to 'y=95.117+331.52'. The 2nd trend line is correct.

Why would this happen? The data set for the 1st series has not. When I add a 3rd, 4th, ... 7th series, they too are messed up.

The data subset is generated by a VBA search macro. I have confirmed the data is not different. Anyone have any clues here? I have plotted the data on the scatter chart, then manually added the trend lines, with the same results.

Thanks for any help.

Welcome to the forum.

Please post workbooks, not pictures.

Thanks.

Posting the workbook won't work, it's 2.8 megs, plus there is confidential data contained there in.

Here is the code I use to generate the plot data and the trend lines. There is a routine above this code that searches about 200 columns of various depth looking for matches entered in a userform. The x and y data are stored in 2 strings, separated by commas. I have stepped through the code, and watched the chart as it's being generated. After the first series is created, the trend line is correct. After the 2nd series, the trend line changes to an altered equation. I have tried commenting out code to find out what is going on, but it has not yeilded anything.

    For iLooper = 0 To lbDate.ListCount - 1
        Application.StatusBar = " Generating Chart " & Int(((iLooper + 1) / (lbDate.ListCount)) * 100) & "% Complete"
        With ActiveChart.SeriesCollection.NewSeries
            If Not chkTrend Or lbDate.ListCount = 1 Then .Name = "=" + Chr(34) + lbDate.List(iLooper) + " Data" + Chr(34)
            .ChartType = xlXYScatter
            .Values = "={" + ArrAxisDataY(iLooper) + "}"
            .XValues = "={" + ArrAxisDataX(iLooper) + "}"
            If Not chkTrend Then
                .MarkerSize = 3
            Else
                .MarkerSize = 2
            End If
            .MarkerStyle = 8
        End With
        If chkTrend Then
            If lbDate.ListCount > 1 Then
                For iCount = 1 To ActiveChart.SeriesCollection(iLooper + 1).Points.Count
                    With ActiveChart.SeriesCollection(iLooper + 1).Points(iCount)
                        .Format.Fill.Solid
                        .MarkerBackgroundColor = rgbColor(iLooper)
                        .MarkerForegroundColor = rgbColor(iLooper)
                    End With
                Next iCount
            End If
            With ActiveChart.SeriesCollection(iLooper + 1).Trendlines.Add
                .Type = xlLinear
                .Name = "=" + Chr(34) + lbDate.List(iLooper) + " Trends" + Chr(34)
                .Border.LineStyle = xlContinuous
                .Border.Weight = xlThick
                .Border.Color = rgbColor(iLooper)
            End With
        End If
    Next iLooper

There's nothing I can do with your code. Good luck.