in the rock make free climbing impossible, and by avoiding purely mechanical techniques (such as repetitively drilling bolts). Today, many routes which were originally done using aid are being climbed free by a new generation of climbers with immensely improved skill, physical ability, and significantly advanced equipment including modern ropes, high-friction rubber shoes, and modern camming devices. Some of the techniques used to achieve free ascents of aid routes, for example placing extra bolts for protection (retro-bolting), are now sometimes thought to have "polluted the pure spring of mountaineering" by destroying the route as it was climbed by the first ascensionists. The solution is often a compromise in which an absolute minimum of bolts is added to allow safe protection for free climbers, while not totally destroying the challenge of the route as an aid climb. However, as with most compromises, this is not a solution that satisfies everyone. Grading The A grading scale (A for 'artificial' or 'aid') incorporates difficulty of placing protection, and the danger associated with falling. The original scale was a closed gradation scale from A0 to A6, modern aid climbers have adopted "new wave" grading which compresses the scale but still uses A0–A5. A parallel scale of C0–C5 has been used to describe routes which can be climbed clean. Clean in this context refers to routes that can be completed without a hammer and the associated pitons even if the route still uses previously installed expansion bolts. A0 Pulling on solid protection, often without the use of étriers. A1 Easy aid, no risk of any piece of protection pulling out. Safe falls. A2 Moderate aid. Short sections of tenuous placements above good protection. A2+ May include easier A3 moves but is not hard enough to be rated as such. A3 Hard aid. Involves many tenuous placements in a row. A3+ May include easier A4 moves but is not hard enough to be rated as such. A4 Runout, complex and time-consuming. Many body weight placements. A4+ May include easier A5 moves but is not hard enough to be rated as such. A5 Serious, hard aid with huge falls and possibly lethal results. A6 psycho aid, all placements body weight only including the belay anchor. Literature Long, John and John Middendorf, Big Walls, Chockstone Press, Evergreen, Colorado, 1994. McNamara, Chris, "How to Big Wall Climb", Supertopo, South Lake Tahoe, California, 2013. References Types of climbing Types of