Interpret odd voltage readings

[Greenmamba]

                
                 Interpret odd voltage readings
            

            

  I hope someone can shed some light/help me. Long story short, changed the

plugs a week back, right hand bank of NGK iridiums came out
considerably blacker/oilier than the left bank of plugs. Coupled to poor
fuel/mileage, I eventually got my FreeSSM to extract readings, mainly
around O2/lambda settings. I'm going to try attach 5 screen shots, first
2 on a hot engine, the last 3 cool engine. Engine idling.

The voltage on both sensors readings seem very low to me - less than 0.5
volt at best. Is this OK or not, and if not what would you suggest?

Also, let me know if there are other readings which I'd need to get if what I've looked at so far, is meaningless.

The car has 156k miles and I've been thinking of replacing the front O2 sensors on the cats.
        

Cheers