Just to bring some closure to this thread...
Jerrill sent us some save data that demonstrated the problem. The data showed that the date for the computer was being changed back to a prior date (about 16 months earlier), and this was causing PingPlotter some issues (data from the current period mixed with data 16 months old, then back to the current period 10 samples later).
PingPlotter can probably be set up to better handle a situation like this, and we'll get an change request logged for this.
- Pete