> It has ~5 years of battery life, knows days of the week for the next two thousand years, and has a handy RPN calculator.

I wonder why two thousand years? All the common day of the week algorithms should work as long as the current leap year pattern [1] continues.

[1] (year % 4 == 0) && ((year % 100 != 0) || (year % 400 == 0)