When the presentation gets to the number "seven" you will notice that the7 has a line through the middle of it. That was the way the Arabic 7 was originally written, and in Europe and certain other areas they still write the 7 that way. Also, in the military, they commonly write it that way. The nine has a kind of curly tail on it that has been reduced, for the most part nowadays, to a simple curve, but the logic involved still applies.