Still no luck.
Brand new 2.7 install, default theme, manual install of plugin, still getting the same thing. One post on Aug 10th at 180, second on Aug 18th at 190 (post with graph).
[tally_graph key="Weight" cht="lc" tally_interval="week"]
If theres anything else I can do, let me know.
I'll just use the day interval for now. If you could figure out a way to do a running total method, I really wouldnt even need week. (I only tried to use week to get rid of the blanks that cumulative was causing).
Anyway, hope any of that is useful.