  Semel and Skumanich proposed a method to obtain the absolute electric current
density, |Jz|, without disambiguation of 180 degree in the transverse field
directions. The advantage of the method is that the uncertainty in the
determination of the ambiguity in the magnetic azimuth is removed. Here, we
investigate the limits of the calculation when applied to a numerical MHD
model. We found that the combination of changes in the magnetic azimuth with
vanishing horizontal field component leads to errors, where electric current
densities are often strong. Where errors occur, the calculation gives |Jz| too
small by factors typically 1.2 ~ 2.0.
