This year, I bought the Spouse a Geek Clock for his birthday.
As you can see, the face of this clock is extremely perplexing. For someone like me, that is. For the Spouse, it's wonderful. Shortly after he got it, I caught him in his office, scribbling numbers on his notepad (when he was supposed to be working) trying to understand how the equations work.
The clock came with a cheat sheet. It says - for instance, for the number 3: "A unicode character XML 'numeric character reference.'" The Spouse considers this information useful. It tells me nothing.
The number eleven is "a hexidecimal." Great.
Incidentally, I bought the clock from Uncommon Goods. It's a great place to find gifts. Last Mothers Day, we bought my mother-in-law a bouquet of "rosebuds" made from recycled elephant dung. She loved them.