The other day I was at the Pike Place Market and walked by a street performing pitch and saw this:
Unfortunately Mr. Unity wasn’t there, so I can only form my opinion based on his milk crate stand.
It looks like he does the day of the week birthday calculation. This is something that I’ve personally never understood why is impressive. It’s clearly a math calculation, not a memorization feat (at least when I’ve seen it). And the end result is something that I didn’t know or have any connection to.
I think if it was reversed and you told the magician the day of the week you were born on and the year, and they told you your birthday, it’d be much cooler. However, I’m going to imagine that would ultimately give the magician a 20-25% success rate, unless there some some fishing for where in the month the birthday is.