

Now you put another portal in the pit to your left, direction west. Put a portal on the first platform, and let's call that direction north.

Start chamber 18, and go to the room with the platforms at different heights, where you need to put portals on ever higher platforms while jumping through them, and eventually on the angled one that flings you towards the exit. Jump into A facing east, and you come out of B facing north. Put portal B facing north, portal A facing west, and jump into A facing west, and you'll come out of B facing south. If you start putting portals on the ground in other directions, everything stays logical. So far so good, and consistent with the way portals work. You need to know this for several advanced chambers and challenges, when you jump into one and come out of the other, and have to move backwards to get onto a platform. When you jump into one portal, still facing north and looking down, you will come out of the other portal, looking up and now facing south. You put 2 portals on the ground, next to each other. Picture the following situation: you're standing somewhere, facing north.

Something physical to represent both 2 portals and yourself could be useful. Something about test chamber 18 has been bothering me for a while.
