Comparative electron polarization measurement with a helium electron polarimeter and a high‐precision Mott detector are presented. For these measurements the helium electron polarimeter was calibrated according to theory, whereas the Mott detector was calibrated independently with an improved auxiliary‐target method. The comparison of the experimental results reveals various problems inherent in helium electron polarimetry, such as poor efficiency and problems occurring in precise light polarization measurements. At present, a high‐precision Mott detector is therefore clearly superior to a helium polarimeter with respect to efficiency and accuracy. ©1995 American Institute of Physics.