Okay, so the numbers are indicators of degrees of difficulty. In the US, we use three different measures for difficulty, depending on the type of climbing. These measures reflect steepness of the face (including potential overhanging), number of possible holds, and usefulness of those holds.
1. Bouldering (like Rydra does) uses a V scale, going from V0 (easiest) to V10 (hardest). I've never seen anything harder than V10 at the gym, but I'm sure they exist outside. In the gym I attend, V0 is roughly equivalent to a 5.9 or so, maybe an easy 5.10. But the routes tend to be steeply overhanging, with multiple difficult moves linked together.
2. Free-climbing, like you see when people are roped up and either climbing bolted routes or setting their own protection, use what is called the Yosemite Decimal System. You start with a system of classifying hiking/scrambling, where flat ground is Class 1, easy uphill walking is Class 2, etc, up to Class 5, which requires the climber to be roped for safety because if they fall they can die. Class 5 was originally broken into ten subcategories, so you could climb 5.1 to 5.10, and 5.10 was The Hardest. The grade is generally set to reflect the difficulty of the hardest move in the routes (the crux), although it may score higher if there are multiple difficult moves.
Of course, what happened after the YDS was established (in the 1930s, according to Wikipedia) is that climbing technology improved--new shoes, new ropes, better protection--and we could safely climb routes that couldn't be climbed before. So now the YDS goes up to 5.15 IIRC.
Most indoor climbing starts at about 5.3-5.5, which are basically ladders on a straight-to-slightly-sloped face. Nowadays, I spend most of my time on 5.9s and 5.10s, and because this is common for a lot of climbers, the 5.10s are sub-categorized into 5.10a, 5.10b, 5.10c, and 5.10d. Same with 5.11s, not so much with 5.12s. I've never seen anything harder than a 5.12 at an indoor gym.
Sometimes there will be an added note in the guidebook indicating the risk of injury if you fall: the one to worry about is "X", which basically means there are spots on the wall where if you fall, you will hit the ground and very likely die.
3. Aid climbing, which is big-wall climbing where you actually use the ropes to pull yourself up the wall, uses a different system, looking at the requirements for specialized gear and the possibilities for protection placement. A0-A5, where A5 involves the potential for a fall of 20 meters or more.
Finally, the YDS is not universal; the British and French both have their own systems, and the Australians also have one. So when I climbed in Thailand I got to know the French system, possibly because the first international climbers there were French? I dunno.
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Okay, so the numbers are indicators of degrees of difficulty. In the US, we use three different measures for difficulty, depending on the type of climbing. These measures reflect steepness of the face (including potential overhanging), number of possible holds, and usefulness of those holds.
1. Bouldering (like Rydra does) uses a V scale, going from V0 (easiest) to V10 (hardest). I've never seen anything harder than V10 at the gym, but I'm sure they exist outside. In the gym I attend, V0 is roughly equivalent to a 5.9 or so, maybe an easy 5.10. But the routes tend to be steeply overhanging, with multiple difficult moves linked together.
2. Free-climbing, like you see when people are roped up and either climbing bolted routes or setting their own protection, use what is called the Yosemite Decimal System. You start with a system of classifying hiking/scrambling, where flat ground is Class 1, easy uphill walking is Class 2, etc, up to Class 5, which requires the climber to be roped for safety because if they fall they can die. Class 5 was originally broken into ten subcategories, so you could climb 5.1 to 5.10, and 5.10 was The Hardest. The grade is generally set to reflect the difficulty of the hardest move in the routes (the crux), although it may score higher if there are multiple difficult moves.
Of course, what happened after the YDS was established (in the 1930s, according to Wikipedia) is that climbing technology improved--new shoes, new ropes, better protection--and we could safely climb routes that couldn't be climbed before. So now the YDS goes up to 5.15 IIRC.
Most indoor climbing starts at about 5.3-5.5, which are basically ladders on a straight-to-slightly-sloped face. Nowadays, I spend most of my time on 5.9s and 5.10s, and because this is common for a lot of climbers, the 5.10s are sub-categorized into 5.10a, 5.10b, 5.10c, and 5.10d. Same with 5.11s, not so much with 5.12s. I've never seen anything harder than a 5.12 at an indoor gym.
Sometimes there will be an added note in the guidebook indicating the risk of injury if you fall: the one to worry about is "X", which basically means there are spots on the wall where if you fall, you will hit the ground and very likely die.
3. Aid climbing, which is big-wall climbing where you actually use the ropes to pull yourself up the wall, uses a different system, looking at the requirements for specialized gear and the possibilities for protection placement. A0-A5, where A5 involves the potential for a fall of 20 meters or more.
Finally, the YDS is not universal; the British and French both have their own systems, and the Australians also have one. So when I climbed in Thailand I got to know the French system, possibly because the first international climbers there were French? I dunno.
This Wikipedia page has a pretty good overview/explanation of the rating systems, and a very useful comparison chart at the bottom.