RE: UPC...My unit is a PowerTripp from Costco. Not long ago the voltage screen started jumping all over, much like you are describing. Still seems to work though. I have changed the battey in it once.
Edison just called and said problem is fixed. It was something in the substation that did not reset. This has happened up here before. Last time my dryer motor overheated and shutdown. That is how I found the problem last time.
Voltage at the house is now holding steady at 125.5.