  The physics interpretation of the recent measurements of the spin
polarization of $\Lambda$ hyperons produced in relativistic heavy-ion
collisions is discussed. We suggest that the polarization measured in the
$\Lambda$ rest frame should be projected along the direction of the total
angular momentum that is first transformed to the same frame, and only then
averaged over $\Lambda$'s with different momenta in the center-of-mass frame.
As this improved procedure is not expected to significantly change the present
results regarding the global spin polarization, it may affect the estimates of
the magnitude of the polarization and its energy dependence. Such a treatment
is also generally more appropriate whenever directions in the $\Lambda$ rest
frame and in the center-of-mass frame are compared. Throughout the paper we
deliver explicit expressions for various boosts, rotations, and transformations
of angular distributions, which may help to compare model predictions with the
experimental results.
