Recommended conventions:

left-handed: polarisation opposite to momentum
             P(e-)<0,
             P(e+)<0

right-handed: polarisation parallel to momentum
              P(e-)>0
              P(e+)>0

Studies with: P(e-) = +- 80%
              P(e+) = +- 60%

Precision in polarisation measurement:   two values
                                         delta(P)/P= 0.5 %
                                                     0.25%

                                         if in the right mood: 0.01% 


Anything more needed?