A155s Back To Perfs And Color?

So, I'm going back to perfs and color issues on this page from my old book. I see several different colors and can't figure which is what... and then there is the quizzical note on the top of the page saying 11, and 10 1/2 How can you have a half? and which way am I supposed to be counting... both?
Can someone do a half hour webinar on this please...

Some stamps with this design (Sc 632) have perfs of 11x10 1/2.

What this means the top and bottom perforations measure at the rate of 11 per 2 centimeters length and that the two sides measure at the rate of 10.5 per 2 centimeters.

I would infer that the person who prepared this page, had sorted his stamps so that Sc 632 would be on the page and noted this by referring to the perfs present.

To check this, it makes much more sense to use a gauge than to count. In fact, for these I wouldn't bother counting, I would just use a gauge.

I like the attached pair... very nice.

Which ones? the horizontals or the verticals? And what about the colors? Do you agree that all are 632?

With multiples, or stamps issues with perforation varieties,
it is worth considering establishing a known perforation stamp as a template,
and using that stamp to compare all others on the page.
It makes for easy and rapid perf ID.
A lot easier than using a gauge on each and every stamp.

the horizontal pair.
They look like SC#632
green and yellow green.