I was playing with the astigmatism dial (attached) and noticed something.
Without glasses, i cannot get the two lines to be clear simultaneously.
I can clear the line with the arrow up to 16cm and the perpendicular line up to about 23cm.
When i put the dial even closer to my eyes it is easier to clear both lines but not at the same time… when i clear one line, the other lone gets slightly blurry.
If anyone can explain what is the mechanism that prevents the eye from clearing both lines at the same time or any other insight, that would be awesome!