Fast dual wideband AFR values lower than Flashscan

[camaro427-69]

hi guys

finally got my V8 gauge/log working with my E40 controller in my 05 ls2 Vette and reading all the stuff i need to street log my H/C/I setup.
What is a bit confusing to me is that the fast controller shows 14.5 AFR and the AD1 connected to my flashscan an laptop shows around 15.1 so the flasscan reads a tad more than half a point more than the WB controller.
The wideband is set on high resolution and the values in the formula are on the predefined values what would match the value that even the Wideband screen says. which value is now to trust or do i have to change the PID formula to different values

-- WO2A.AFR_F1
return pid("AD1")*2.78+9.6

any suggestions?
thanks,
pat

[LastCall]

Looks like a Ground offset issue. You can adjust your calculated pid or try to fix the ground issue.

[camaro427-69]

i have built a different funktion into my PID list for BBX logging where i used a value that a guy mentioned in a old FAST WB thread where he had to change the values due to the same problem like i have.
I have a friends LC1 sitting here but i

[joecar]

You can add a constant offset, or you could short AD2 +/- (i.e. making it zero volt input) and add/subtract EXT.AD2 from EXT.AD1 before calculating lambda/AFR.