The Snyder Metric is a move count metric in which every parallel simultaneous movement of the puzzle is counted as one turn, regardless of the puzzle shape or the complexity of the turn. It is more or less equivalent to the Axial Turn Metric, where a movement of any layers (on the same axis) in any direction(s) counts as one turn. Snyder Notation may be used to represent turns using this metric.
The Snyder Metric was invented by Anthony Snyder in 1983. He argues for it as follows: "I have never understood why the turn counting rules/standards follow a 'range of motion metric' rather than an 'efficiency metric'. Solving for fewest turns is a challenge in efficiency to start with, so the metric should also be based on efficiency. In my opinion the most sensible way to count turns is to figure that any parallel simultaneous movement is one turn. This would also make the rules far simpler. Another point is that there are many ways to fine-tune solves by adding more anti-slices. Examples: I far prefer solving the U-Twist (headlights) with R L U2 R' U' R U' R' L' U2 L U L' U, which works out to just 12 very easy to perform turns once you define the anti-slice into the metric (using Snyder Notation the same algorithm: R+o' U2 R' U' R U' R'o+ U2 L U L' U). This requires only 12 parallel simultaneous movements, which is in my opinion more efficient than the 13 turn F U' R2 U R2 U F U' F2 D R2 D' R2. Another example is the H-PLL, which can take just 6 turns using the Snyder Metric."
The following algorithm for a corner 2-twist uses only 12 turns in this metric, fewer than most popular algorithms. In normal and Snyder Notation:
- R L U2 R' U' R U' R' L U2 L U L' U (14 turns HTM)
- R+o' U2 R' U' R U' R'o+ U2 L U L' U (12 turns Snyder Metric)
And the H perm can be solved in 6 turns in the Snyder Metric:
- R L U2 R' L' F' B' U2 F B (10 turns HTM)
- R+o' U2 R'o+ F'o+ U2 F+o' (6 turns Snyder Metric)