Verus scope what channel is reads correct

Hello
While checking a Saab alternator I noticed the channels on my scope all read different
Scope set to 500 MV on ac coupling
All connected to Saab batt positive post +
I also tried the same settings with no test leads attached
3 read different with the red channel flicking between 1.6 & 1.4
Have tried a few time to add photos they don't seem to be uploading yet
Yellow reads. 1.1 live
Green reads 4.9 live
Blue reads. 1.6. Live
Red reads. 1.6. & 1.4
Whitchurch ones correct , on my third scope from snapon they have all read different
Would you guys please try your scopes verus modis edge
Thanks from scott

Looks well within what I would expect, oscilloscopes especially automotive oscillocopes generally aren't great as precision millivoltmeters.
If you want to check the accuracy of scope or voltmeter check it against a DC precision voltage source.

Also be aware unshielded or non-twisted pair leads pick up a lot of induced noise. Slight differences in the routes and lengths of the leads make a big difference to in noise amplitude. To minimise noise the live connetion and the ground connection should follow the same path as close as is possible. For this reason I try use BNC coax or twisted pair for connections where possible and make the ground connection as close as possible to where I connect to signal wire on the car.