Finding data point from graph

I actually feel crazy asking this question but I assume there simply must be something easy I am missing. I have a couple of graphs in the attached spreadsheet and on Oct-10 the graph point drop randomly by around 15% basically throwing the whole graph out. When I go and look at the data the graph is looking at their is no abnormalities to explain it... can someone please help me understand what is going on here because I cannot get it! Thanks
1.xlsx