Learning About Perforations

Can someone explain why this is a 1711c? It does not seem to align with the 11.2 unless I am doing something wrong. The seller said it was a 1711c. I can post a complete picture of the stamp if it's helpful.

Looks like perforated 11 to me. Sometimes sellers advertising is wrong. There are so many listings I have seen where the stamp is not what the seller says. Sometimes I send a message to the seller telling them so. Not sure if that's appropriate or appreciated.

You might want to consider measuring the perfs along a vertical edge of the stamp. The difference between 11 & 11.2 is quite small. The horizontal perfs match both 11 & 11.2 rather well. The longer side will show the difference, giving the perfs time to slowly wander off the 11 scale.

A lot of perforation stories are full of holes.

The stamp you are asking about is Scott 1711, the Colorado Centennial issue.
Scott lists two perforation varieties. They can be differentiated by sight, however because the line-perf variety can also line-up nearly perfect on an occasional corner, it would be good to see your entire stamp and thus erase any doubt as to which one you have. Seeing only one corner is problematic - especially with the gauge images.

I believe the perforation differences can be seen in the corners of the stamps:

Note the "perfect" corner--



Note the "random" corner


Perforations were applied by different devices.

Please do so, it always helps. Here it would allow all four corner perforation to be examined.

What do you think?

I think the one on the left is the 1711c, bullseye perf 11.2
and the one on the right is the 1711, line perf 11.

Look at the bottom corners of the righthand stamp. In order to be bullseye perfs, the horizontal and vertical perforations should line up perfectly in even rows and columns, but in the bottom corners of the righthand stamp, they don't line up, they are askew/random, like they are off half a beat.

The stamp on the left looks like a better candidate for 1711c. How does it compare to the other on the perf gauge? As you can see, the vertical perforations on the two stamps are not the same gauge.