Figure: (a) Absolute value of the physics asymmetry ε_phys and (b) azimuthal angle between the transverse spin component and the vertical direction, observed during the rotator currents adjustment at STAR. The adjustment was performed iteratively, in the series of three-run steps. Each run was ~9 min long and yielded ~70-80 M triggers, recorded by the fast readout system based on scaler boards. Without spin rotators, the stable direction of the proton spin at RHIC is vertical (pointing upward) and the expected magnitude of the physics asymmetry was 0.04 for both beams during that running period. The last four runs demonstrate that the beam became almost fully longitudinally polarized at the STAR location, with the residual relative transverse component of 5% and 2% for the yellow and blue beams, respectively. Several additional small adjustments were performed in the following days (not shown in this figure) to keep these residual components at the low levels of <5%.