What does it mean in measuring terms to not exceed ten inches across?

I would assume that a very broad shouldered man wouldn’t be able to wear a regular jacket, so if the measurement exceeded 10 inches, he would need a jacket that was a bit bigger than a regular to take that into account.

I’m left guessing too. I looked at a number of videos but found none other than the one you referenced that even called for this around-the-arms measurement. I worked in a menswear department for a time while I was in college. 36 R or 42 R refers to regular length, not shoulder width. For a tailor made suit, if the customer had extraordinary upper body development, then the standard chest measurement alone isn’t enough. The suit will need to be wider in the shoulders to accommodate the wide spread of the shoulder bones and the upper arm and shoulder muscle development. While the video isn’t very clear on this, I am guessing it means that if the chest measurement under the arms is 36 inches and around the outside of the arms is greater than 46 inches, then the standard 36 Regular or 36 Long or Short pattern needs to be tweaked to provide room for those broad shoulders.

First chest measurement circumference (under the arms) is 36 inches.

If the second measurement around the shoulders is more than 46 inches, the 36 jacket will be too tight.

I thought that, too, @gailcalled. What she meant to say was “greater than a 10” difference”. But I don’t see how it could be such a small difference when measuring over the arms. In order for that “over-the-arms” measure to be less than 10” greater than the basic chest measure he has to have stick arms. I’m no Charles Atlas, but measuring over either of my upper arms is going to add about 7–8” minimum to the chest measure. (I haven’t been able to wear a 36” jacket since junior high school.)

It would have been helpful if she had mentioned what that second measure was.

Here’s the same couple doing the same measurement. This time she mentions “difference”.