Curious about these sights as I don't have one - my Long Branch came with a CMk3.

I assume "Singer" refers to Singer the company as a maker of these sights. I also assume that numerous companies other than Singer also supplied these sights.

1. Why is this variant of the leaf sights generically (it seems to me) referred to as "Singer sights"? Because Singer made the majority of them? Something like that?

2. As a click adjustable military sight for the No. 4, what distance does one click subtend at 100 yards? I suspect it won't be anything close to an inch (1.047") or a half of an inch.