WaferLot nTot  nOK  nB2  nC1  nC2   yield    yieldOpt
    28   5432 3785 1294  353    0   69.7%   76.2%
    29   6512 4506 1288  718    0   69.2%   80.2%
[yield=nOK/nTot yieldOpt=(nTot-nB2)/nTot]