Fable
The altimeter in the mountaineering coach's hand and a full map book
Two groups arrived at the mountain camp. The first held an altimeter showing 3,200 meters and went around telling everyone the camp was at level three. The second pulled out an atlas and said the mountain was divided by altitude into seven climbing zones, from meadow to glacier, each with different equipment requirements and weather risks; level three covered 2,500 to 3,500 meters and required windproof clothing and trekking poles.
The two groups argued all morning. Those holding the elevation table insisted that level three was 3,200, very simple. Those holding the map said you are reading a point as a region; 3,200 is only a value within the level-three region that can fall anywhere. Neither side accepted the other, and the guide stood in the middle, at a loss.
The real trouble came with equipment procurement. When the equipment supplier heard the word "level three," they sent six sets of high-altitude cold-weather gear to the team holding the elevation chart—they assumed level three meant the glacier zone on the map, but in fact 3,200 was only the shrub belt on the mountainside, and high-altitude cold-weather gear was completely unnecessary. The team holding the map equipped windbreakers according to the standard for a level-three area, which was just enough. The equipment supplier came to return the goods, saying that the same word in your mouths did not mean the same thing.
That evening the guide drew a diagram. On the left he drew a ruler, marked with seven intervals, each with a name, a range and corresponding rules. On the right he drew a dot, and said the dot falling on the ruler is the current reading. He told everyone: a level is a dot, a single altitude reading; a level system is the whole ruler, with seven gradations. The dot falls on the ruler, but the dot cannot replace the ruler.
Later, the team needed capability assessment. The person holding the altimeter could only tell others the current altitude, but couldn't say what equipment would be needed to climb higher next. The person holding the map could plan the route from the start, knowing what conditions level four involves, what risks level five has, and that level six requires an oxygen tank. The guide said, what you need is not just to know where you are now, but also to know what you'll encounter as you climb.
A notice was posted on the camp wall: whenever anyone says what level our system is at now, they must also cite the corresponding level definition, evaluation method, and scope of applicability. They cannot just say a number. A number without its ruler is just noise.
A few months later, a newly arrived team said at camp that they had done a Level 3 autonomy test. The guide asked what capability, what scenario and what limitations Level 3 corresponds to. The other side flipped through the report; the report had only a number, with no corresponding definition table. The guide said then what you tested was not a level system, just a test score.