The last letter of the code shows which mental muscle appears to the right of the line. That is: If J, then (T or F) appears to the right If P, then (S or N) appears to the right

Bad Joke: A lady arrived at a train station to catch a train at 5:20. The clock outside the station said "5:12", so she went and bought a coffee. Two minutes later she walked on to the platform, to see the train departing and the platform clock showing "5:22". She asked the platform attendant why the clock showed the wrong time, to which he replied: "why would we need two clocks if they showed the same time?"