If you don't have one, get a perforation gauge. They're cheap. And use it. When you think you have identified a stamp, make sure it has the correct perforations. I didn't, and made an ass of myself, trying to sell some rather expensive stamps on
ebay, when the stamps were a much cheaper version, identical in appearance but with different perforations.
And I think someday soon you will want a Scott Specialized. Buy one a few years old. Much cheaper.
Don