Mine still jumps all over the place, a lot less now but a lot earlier in fermentation. My guess is, the CO2 and the krausen all made the hydrometer sit at weird or different angles. I've obviously ignored all readings in the 1.18 range, but I'd say 45% of the readings were at this level, which makes the graph really messed up.
What's even weirder is that every time the SG showed a reading of 1.18, it also read a slightly higher temperature. Whenever the readings were in the proper SG range, the temperature read around 64-65... But when I got the erroneous SG readings the temperature read about 72. Not a huge deal and had a pleasant overall experience with the device, but I really wish I was able to save the graph without it looking like a crazy crayon drawing made by a little kid.