Series showing incorrectly on scatter chart

[Guest]

I am plotting scatter charts in Excel 2003. I have a diagonal line on each
chart (to show the line x=y), which I put there by adding a "dummy" series -
(0,0), (1,1), (2,2) etc. to give a straight line. However, on some of my
charts this shows up as not one but two straight lines - one showing the
correct x=y line and another one which also goes through zero but has a
different slope. I can't work out why this happens or how to fix it. If I
format the data series to show data markers, all of them lie on the correct
line and none on the incorrect line. I have made sure I haven't inadvertantly
added an extra series to my chart - the incorrect and correct diagonal lines
are definitely part of the same data series. This problem happens on only a
couple of my charts (the ones with the lowest values), even though I have
several other charts linked to the same "dummy" series.
I hope this makes sense. Has anyone got any ideas on how to fix this?

 

[Bernard Liengme]

I wonder is you have a tendline added to the non-dummy values. Can you
delete the incorrect line?
Would be happy to look at chart if you send file to my private email
best wishes

 

[Guest]

Hi Bernard,
Thanks for that suggestion but it doesn't seem to be a trendline. If I
delete it, it also deletes the correct line. I have emailed you my
spreadsheet - it would be great if you could take a look.
Thanks,
Amy