Some 581's Or 578's Or 552's (I Think)

I think I have these narrowed down to 3 possible types depending on perforations. I downloaded a free perforation gauge online. Not sure if it can accurately measure these or not. Do I need a real gauge or can I do it with my free one? These look like they could be different issues they have different color for sure. Any comments welcomed. Thanks. I also have a ruler that measures cent. I just don't know how many perfs to cent.

The number of perfs per centimeter will depend on the gauge of the perforations. For example, if there are 11 perfs in a 2 centimeter (20 millimeter) distance then the gauge for that side of the stamp is Perf 11 (10 perfs per 2 cm is Perf 10, etc.).

Thanks I can figure it out, I believe.

The left pair looks to be Sc 552 and the other looks like sc 635. The left pair look smaller which comes from flat plate printing. There is probably some green ink under the gum which can be seen(it might take a magnifying glass). Also the perfs don't line up between the two pairs. That would indicate the perfs are 10.5 for the right pair. You shouldn't see any ink on the back of the right pair which is another indication they are made with a rotary press.
The perf gauge, a good magnifying glass, and something to check watermarks are your first purchase. Without the tools you will be lost on determining what you have. You will be even more upset if you were to sell or trade something only to find out it was a rare variety. You can read all you want but there isn't anything like holding them in your hands and making the discovery.

Thanks, you are right there is green on the back of one of the pairs, don't need a glass its pretty obvious. I will get a good gauge. I used my centimeter ruler and thought I counted 10.5 on one side of one pair. I think the one I am looking for is perf. 11x10.5. One thing is for sure there is not much difference between 11 and 10.5.