first encounter to binary numbers

late post again... my computer broke down...
On Tuesday last week we learned how to overlay the barracuda on the edge of the circle so it rotates on its tale instead of its center of its body. After that, the barracuda looked actually like a second hand of a clock!! Also, when the barracuda was pointing down the barracuda stopped rotating and produced an image stop. I actually do not know how stop sign pops up when barracuda points down. I think it is produced from this function:

(define (key-press im k)
  (cond
    [(equal? k "down") (stop-with STOP)]
    [else im]))
but still, i think i have to study more to figure out how this function works.
On Thursday of that week, we learned about binary numbers. I have seen and heard about binary numbers but never used them or convert from binary numbers to the number in ten base or the other way around. It was very interesting how all the numbers that we commonly use, could be turned into number 1s and 0s and represent same meaning. We learned how to add and subtract using binary numbers. I practiced more on subtract and add binary numbers on my own time.  However, i am really not used to using the binary numbers and again, i need more practice using it. This week is reading week and i am planning to work on Wikipedia and try to finish the second part of the assignment before i go to school again.