I posted this a couple of years ago...but can't seem to find it so I thought I would repost the link. Pages 14-15 are what you really need to know about how to troubleshoot timegrapher plots....enjoy!
https://www.witschi.com/assets/files/sheets/Witschi Training Course.pdf
https://www.witschi.com/assets/files/sheets/Witschi Training Course.pdf