[en] Magnetic probe measurements show that the flux trapped into the neutral sheet radius R sub(o) at the early phase of the reversed field theta-pinch does not decrease monotonously but oscillates. We proposed a model that the oscillation may be caused by the off-diagonal element of the ion pressure tensor P sub(r theta)sup(i) which may also drive the plasma rotation. The accuracy of probe measurement was confirmed to be less than 10% by using the excluded flux. The experimental data are compared with the results of one dimensional hybrid code. We found the agreement between the two is fairly good. (author)