WaferLot nTot  nOK  nB2  nC1  nC2   yield    yieldOpt
    28   5432 4121 1187  124    0   75.9%   78.1%
    29   6512 5303  935  274    0   81.4%   85.6%
[yield=nOK/nTot yieldOpt=(nTot-nB2)/nTot]