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*See the [Aura Definitions](https://hackmd.io/-5NhDyekTJWH4NmPD3xBTg) document for more detail on the meaning of the terms used.*
## Overview
Subjects, Players, Trainers, and Managers can achieve levels by being evaluated by Players, Trainers, or Managers.
Levels are team-specific and set by team captains. A team must try to create useful levels to increase their chance of being included in leagues[^1].
Levels are a convenient way to consistently measure quality. For example, "subject level 1" communicates a certain level of quality about the subject. As conditions in the network change, the underlying requirements ([overall score](#Overall-score), [minimum ratings](#Minimum-ratings)) for a subject to achieve level 1 might change, but the quality conveyed by that label will remain constant.
## Level requirements
### Overall score
Each level defines an *overall score* needed to achieve the level.
$$
overall\_score = \sum_{n=1}^{num\_evaluators} \max(overall\_score_n \cdot confidence_n \cdot sign_n , cap)
$$
* $overall\_score$ is the overall score the evaluator received from their own evaluators, [except in the case of managers](#Manager-energy-differences). An evaluator must have positive energy for their evaluation to contribute to the overall score.
* $confidence$ is the confidence rating given by the evaluator.
* $sign$ is $1$ or $-1$ , indicating a postive or negative evaluation.
* $cap$ is the maximum allowed contribution by a single evaluator to the overall score. This is defined with the level.
### Minimum ratings
A level may define minimum rating requirements. A requirement defines both a minimum rating and a minimum evaluator level. Requirements can be combined with logical AND and OR operations.
For example, Team BrightID might attach the following minimum rating requirements to its subject levels.
* Level 1: one low+ confidence rating from one level 1+ player
* Level 2: one medium+ confidence rating from one level 1+ player
* Level 3: one high+ confidence rating from one level 2+ player OR two medium confidence ratings from two level 2+ players
* Level 4: one high+ confidence rating from one level 3+ player OR two medium confidence ratings from two level 3+ players
Player, Trainer, and Manager levels have their own minimum rating requirements.
## Manager energy
Energy is a special name for the overall score for managers only, and it's computed differently. Energy flows between managers for a limited number of iterations using a weighted SybilRank algorithm. The seeds in the algorithm are the team captains. Manager energy flows from one manager to another proportionately to the confidence they have in their positive evaluation. When a manager evaluates a new manager positively, it reduces the energy flowing to other managers they're already evaluating. This is different from trainer and player energy, where one evalution doesn't diminish other evaluations.
Despite the differences in how they receive energy, managers can still receive levels, including [negative levels](#Negative-levels). To bootstrap manager levels, team captains are exempt from [minimum rating requirements](#Minimum-ratings) and achieve their levels based on [overall score](#Overall-score) alone.
## Level zero
Level zero indicates a provisional role. Anyone can choose any provisional role for themselves, but to achieve a postive-numbered level, they need to receive evaluations and meet the [requirements for the level](#Level-requirements).
## Negative level
It's possible for a subject or participant to receive a negative level if their [overall score](#Overall-score) is negative. [Minimum rating requirements](#Minimum-ratings) aren't used in the negative level; only the overall score is considered.
[^1]: A league is an entity in Aura that aggregates levels from one or more teams to create its own set of levels that are easy for apps to consume. Leagues track the rise and fall in utility of different teams so that apps don't have to. For example, BrightID (League) levels 1-3 might correspond to what were previously called Aura Bronze, Silver, and Gold.