You dont need to install a additional meter,
As I said above you can get stand alone temporary power monitoring equipment.
We use it regular at work for finding odd problems.
It will monitor power, voltage, current etc every second (or few seconds over longer time frames) and give you a excel spread sheet of all the data with dates and times.
This will allow you to narrow down the problem to smaller avenues of time periods and if indeed there is any problem at all or just your meter going mad!
As I said above you can get stand alone temporary power monitoring equipment.
We use it regular at work for finding odd problems.
It will monitor power, voltage, current etc every second (or few seconds over longer time frames) and give you a excel spread sheet of all the data with dates and times.
This will allow you to narrow down the problem to smaller avenues of time periods and if indeed there is any problem at all or just your meter going mad!