W
White Room
It took me about 3 days to get my position correct & my eye right on the line under the bar, within the week it was like second nature.
You can drop the wheel down onto the mark to double check but I don't do it as you learn to trust where your mark is lined up.
It's hard to explain but if you stick with the Sigma you won't go back to a Rubi,
I don't like the pull cuIt Sigmas, they aren't for me.
I tried one and was never going to get used to it