Scott 37 On Cover...different Cancel.

I realize that Robert, I have several, plus one I made myself. Since people here are talking about different physical gauges and doing perf measurements, I am showing the importance of calibration.

I am with you though, I think electronic measurements can give better results.

Respectfully disagree, the quality of a scanned image varies. First, users should be using only a quality flat bed scanner. (Those scanner which feed the item through a paper path can introduce dimensional variances.)
Second, you have to make sure the user is using only the optical resolution when scanning and not some software interpolation.

And while I would not expect dimensional errors to be introduced by the stepper motor, in most scanners each horizontal line is projected into the sensor array via a lens. It is possible that some dimensional lens errors can be introduced especially if the target is not centered on the bed. Lenses can cause either a pincushion or barrel type distortion, so dimensions taken from the center of the field can be slightly different than those towards the edge of the scanning field.

Lastly, we also have to assume the user has never used any other kind of software manipulation, saved the file in an uncompressed format, and knew how to scan at the correct resolution to begin with.

So I would say that it is possible to get some accurate dimensions from a flat bed scanner, but it requires a fair amount of technical understanding, knowledge, and skill.
Don

Yes, I agree with that Don. That is why I said "CAN get better results."

As you can see from the above posts, a similar "amount of technical understanding, knowledge, and skill" is required to get accurate readings from a physical gauge, which includes making sure that it is calibrated.

Brian

Here are two more covers I found with late dot usage. One is 1886, the other 1890. The 1890 is partly cut by the perforation. Perhaps it is not even a dot, just ink splatter. The 1890 also has part of the margin inscription at the top.

It is hard to measure the perforations on cover, but both appear to be 12.1.