(Bracketing) First step in Jackson cross cylinder

The 1st step of the Jackson cross cylinder is bracketing. In bracketing we just confirm that either our patient is astigmatic or not.
In bracketing we Put handle of Jackson cross cylinder at different axis like we put handle at 90 degree, when ahndle is at 90 degree then at position 1 the minus red line would conside at 45 degree and plus back line will conside at 135 axis. And after flipping the handle at the same position the minus red line would conside at 135 and plus black line will conside at 45 degree.
So with putting the handle of the JCC at different positions like 90 and 135 we confirm all the expected axis 90,180,45 and 135 of the cylinder.