This metric is different from others mainly because “slice” moves (any turn of a middle layer on the cube) count as 2 turns, and half-turns count as 1 move.
Keep in mind that God’s Number is only 20 for standard 3x3x3 Rubik’s Cubes. For others, God’s Number varies—and in some cases, it hasn’t been found yet.
R (Right): The side facing to the right. L (Left): The side facing to the left. U (Up): The side facing up on the cube. D (Down): The side facing downwards. F (Front): The side facing you. B (Back): The side facing away from you. Apostrophes denote a counterclockwise turn, so a counterclockwise right spin is R’. 2 turns of the cube (or 180-degree spins) are denoted with “2,” so turning the left side twice would look like F2.
