I don't know if I can explain this, but I'll try. I use both garmin connect and training center. Both give different sets of data and I like the grade portion of training center. I noticed that when I point to a specific spot on a loop I've ridden that the gps data will actually show a negative grade % when I know this particular area is a slight grade leading into a hill. I guess I don't understand fully how the data is collected and how it is displayed and wonder if someone cane shed some light on why the numbers don't seem to reflect what the actual grade is and how the graph is displayed.