Well, that helped, a little. I think what you are referring to is the value "Fuel trim or lambda" plotted in blue on the attached graph, which is from my S500 idling. It looks to me like the computer records two data values, the sensor voltage and the fuel trim, which is a measure of the correction needed at that particular instant.

Most the fuel trim values in the plot are between -2 and +2, which I assume is a %, so I don't know how to relate that to your value of 64. Maybe that's the raw value of "B" in your equation. But that doesn't make a lot of sense, since plugging 64 into the equation

Short Term Fuel Trim% = .7812 * ( 64 -128 )
STFT = -50 (rounded)

Even if the 64 is a hex value (100 decimal), plugging 100 in gives a value of -21.9.

Maybe someone who understands this stuff will enlighten us.

Attached Thumbnails

 

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe