Scanmaster and voltage readings

[cottonpicker14]

Scanmaster shows the battery voltage which flucuates from 13.1 to 13.9 and is constantly changing.
I checked the voltage at the battery with a voltmeter and it shows a steady 13.9 with no flucuation and a steady 14.1 at the alternator.
Is it common for the voltage reading on the scanmaster to jump around or should it show a steady voltage. The reading was taken at idle with no accessories on.
Thanks

 

[Razor]

Scanmaster displays what the ECM see's. Understand the voltage is read of the ignition circuit after the ignition switch. It will always read lower.

HTH