What the Rubik's Clock is
The Clock has nine dials on each side, four pins and four wheels at the corners. Pushing pins up or down decides which dials turn together when you turn a wheel. The goal is to set all eighteen dials to twelve o'clock.
Reading a Clock scramble
Each move names which pins are up, then how far to turn: UR4+ means the up-right pin is up, turn four hours clockwise; ALL2- means all pins up, turn two hours counter-clockwise. U, R, D and L mean the two pins on that side are up. After nine moves, y2 tells you to turn the clock over, and the last five moves are made on the back.
Start from a solved clock with every dial at twelve, and turn the dial each move refers to by exactly the hours given.
How the scramble is generated
Every move turns by a random number of hours, so the dials end up in a random position. The layout of nine front moves, y2, then five back moves is the notation the WCA uses for the Clock today.
Practising the Clock
Clock solves are mostly about planning: knowing which pins to set and how far to turn before your hands move. Use inspection to plan the first side, and time solves in fives to see your average.