Why the scanner its reading 1 point off the WB?

[=fast=]

This is the second time that happens to me, My NGK AFX its reading 13:8 and my scanner its reading around 14:6.
Even at WOT the scanner reads 12:2 and my WB reads 11:2.

I don't know what happen last time i stop tuning it due to work for a couple of weeks when i got back to work on it it read the same.

I try doing my own on the user defined for my WB and it read the same. Who had this problem before, or what can cause that?

The weird thing its that i plug it at a friend truck and it read the same.

[schpenxel]

Make sure your connections are good, especially the grounds

You can change the offset portion of the formula to get rid of the difference. If it's just randomly changed then I'd first try to figure out why though first.. if you can't find a reason, just change the formula.