Well, here's one for the books

We're anticipating my son's annual visit, which is coming up in less than two weeks.  We like to select one day during his visit when we invite Cliff's brothers, nephews, and others who might want to see Jim and his family while they're here.  
Cliff's brother, Don, was asking which day that would be; he'd like to plan on being here.  So I looked at the calendar and then sent my son a message on Facebook:  "Let me know if this is right: you will be traveling here on Saturday, the sixth. So you should arrive here Saturday night. I'm trying to figure out the best time to get all the family together (Don and his kids, etc.). Best I can figure, it would be Sunday the 7th. Or else Saturday the 12th. What do you think?"  
This morning my son had answered me like this:  "By my calender the 6th is Sunday, and that's when we are heading up there. We both work on Saturday.  The following Saturday is probably best."  
I went to the kitchen to look at my big Flylady calendar.  I fell off the Flylady bandwagon long ago, but I do like her overpriced calendars; you can see the numbers clear across the room, and the older I get, the more I appreciate that.  
How could it be?  My calendar had that Saturday as the 6th.  I rubbed my eyes, checked the month and year, and decided my son was crazy.  I checked the calendar on my Mac, and lo and behold, the sixth was Sunday.  Now who's crazy?  
I finally figured out the problem.
  

Look at the date of Saturday, then look at Sunday.  There are two 6ths there.  No wonder I stopped following Flylady:  She can't be trusted!