NUMBER CRUNCHING
The A-B-C's (and D's) of rock-climbing

To rate the difficulty of rock routes, North American climbers use a numerical scale called the Yosemite Decimal System (YDS), refined at California's Tahquitz Rock in the 1950s. Roped, technical rock climbing is considered "fifth class" and was originally a closed scale broken down into 5.0 through 5.9. (Steep hiking is second class; highly exposed scrambling that might require a rope is fourth.) When climbs harder than 5.9 emerged circa 1960, the system expanded to include 5.10, and then 5.11 … and up through today's 5.15. In addition, 5.10-and-beyond climbs take one of four a, b, c, or d sub-ratings, with d the hardest. Other ratings might be appended for the length of the route and the reliability and spacing of protection.

As you move higher in the YDS, the rock invariably steepens, the holds shrink and grow farther apart, and there are fewer rests. In Yosemite, known for its sheerness, the ratings can also reflect a pitch's overall physicality, if not its hardest move. Here are some seminal Yosemite climbs at each of the higher grades:

5.10 Wheat Thin (5.10c): This 60-foot climb involves continuously laybacking along the edge of a flake, the climber shuffling his hands and walking his feet up, often at waist height with no hand-free rest ledges.

5.11 Butterballs (5.11c): Eighty feet long, this route is dead vertical, with a finger-width (0.75–1.25 inches) fissure splitting a blank face, and some relief in the form of small foot edges. The climber ascends by finger locking: inserting his fingertips, thumb either up or down, and then twisting to complete the grip.

5.12 Tales of Power (5.12b): This thin, 60-foot crack overhangs for 20 feet. It requires a sustained section of butterfly jamming, in which the climber must contrive a hold by making a modified "A-OK" sign, stacking the middle and ring fingers atop the tip of the thumb and inserting this digital wedge. Your feet go in the crack, too, camming with a twist of the ankle.

5.13 Phoenix (5.13a): A past-vertical, 140-foot crack that's conquered via tight hand jams—hand inserted into the crack and then flexed, to oppose the fingers and the back of the hand.

5.14 Houdini Pitch, the Nose (5.14a): On this dihedral, you have to press your body against its walls and engage in a 180-degree contortionist's turn, scootching inch-by-inch like you would up the inside corner of a building.