you can alter the all time record values by going to view > all time records and there is a “set values” button on that screen which opens another window allowing you to change values.
when you have corrected your log file you can then do “convert log files to graphs” to correct the graph data.
Only one problem left … on the All Time Records, near the bottom of the list, I’m still left with “July minimum temperature” of 0.9F instead of what it actually is. I can’t seem to change that.