@NikeDattani, sorry but the paper that uses "A" is part of a book chapter that belongs to someone else and he is not around because of the pandemic. It doesn't say any more than the paper I provided a link to though. I can't find anything that provides more detail.
@NikeDattani, yes each row is a different time. Thank you for pointing out the Wikipedia article. We saw that but couldn't understand anything new from it.
