While it may sound simple, wait until you see the whole contraption in action. It’s amazing how much patience one person can have figuring out the pattern required to form each digit of the current time. Let’s not forget, the numbers have to change before time is up (the clock would be pretty useless if it took more than a minute to adjust).
The clock took Hans several months to build, and after multiple requests, he has considered releasing the instructions required to build the clock. Until then, enjoy a video of the clock in action: