You could see a fairly large section of sky from each of the two windows if you were close to them. I agree about the "precomp", and remember the Nav craning his head around the windows when a star stubbornly refused to appear in the sextant. As you suggest, he was probably checking whether the sky was clear in that area and to see if the star was visible at least approximately where it should be. If not, he'd try another star or re-check his figures.