see the difference: cross your eyes till the images overlap and form a third image. Then try to focus on the third/ middle image. What is different will "pop" out. Although some people might not be able to do it, like rolling your tongue.
I have figured out that 33 is the distance from the Eiffel tower to the airport and that fr is France and CDG is the airport code, but I cant figure out which airport to use for the colosseum.