I'm periodically seeing negative numbers in the Historical Statistics of some Bandwidth Gauges. I don't think this is a device issue (3Com 3824 GigE switch) as other reporting systems (i.e. MRTG) aren't seeing this. It looks like it might be a reporting error in the GUI even.
I should mention that I'm running an Eval version of the Engineer's kit and this is one thing that's put me on the fence about buying... I would like to be able to trust the numbers I'm seeing, call me crazy.
-2s within chart exports are place holders. They represent that there was no poll taken at that time. 0s could not be used because a 0 represents a poll where the collected value is 0. For example, if you are looking at a chart with an interval of every 1 minute but you are collecting statistics every 5 minutes, then your export would be something like four -2s and then a poll value, four -2s and then a poll value, etc.