Strange IPK figures

[chipsceola]

Just seen ZTT post about mpg on IPK computer. Don't often reset mine but do check figures quite frequently. In past week without being reset the range figure has been well overstated, yesterday it showed 408 miles, and 12 miles later having been rest twice dropped to just 93 miles, at a point where on the fual guage I would normally expect a low fuel light.

Plenums are dry and clear due to regular checks as precaution, not done a battery reset but will watch situation after next 2 refuels to see it corrects itself, unless anyone can throw some light onto this.
Chips