Thank you. I was so confused about where the number 1242 came from. The number 414 isn't in the entire article.
That's because the author made a calculation mistake. He wrote "412" instead of "414".
Even so the base number doesn't show up until most of the way through the lengthy article, with no explanation. Even after reading all those words I didn't understand the critical fact that there was a base size in dots that was different for each model. Everything before was 320 or a multiple.