# Instructions on logic of Overview
A phase value is an aggregation of retention over a period of time, which helps you quickly learn about data performance. This chapter is dedicated to explaining the computational logic of phase values. You may find corresponding computational logic based on the definitions of analysis metrics.
# Logic of built-in analytical metrics
The retention analysis model computes the following built-in analysis metrics regardless of whether Also Show is enabled or not, and the computational logics of corresponding phase values are as follows:
| Analysis metric | Default computational logic | Optional computational logic |
|---|---|---|
| First Event Number | Sum, namely simple addition of different date data | Average, namely arithmetic mean, Sum / Date range |
| Rentention Number | Sum, namely simple addition | Average, namely arithmetic mean, Sum / Date range |
| Retention Rate | Weighted average, that is, (simple addition of Rentention Number) / (simple addition of First Event Number) | - |
| Churn Number | Simple addition | Average, namely arithmetic mean, Sum / Date range |
| Churn Rate | Weighted average, that is, (simple addition of Churn Number) / (simple addition of First Event Number) | - |
# Logic of Another metric
For the Another metric involving different definitions, phase values will adopt different dafault computational logics to adapt to actual business scenarios.
- only entailing the metric of returning users
| Setting of Return user's performance | Default computational logic | Optional computational logic |
|---|---|---|
| Equation or a non-equation that does not use the "average per user" computational method | Average Arithmetic mean of the return users metric across different dates. | Sum, simple addition of different date data Weighted average, equal to average in this condition |
| Based on the "average per user" method, i.e. total per user, user average and accumulative user average. | Weighted average For example, the phase value of total per user is equal to (total times of D1+total times of D2+...)/(number of users of D1+number of users of D2+...) | Sum, simple addition of different date's average data Average, Arithmetic mean of Sum |
The phase value is computed by the arithmetic mean method by default, you can switch to Sum.
- entailing "Return users' performance" and "Metric on Initial date"
| Setting of Calculation and display | Default computational logic | Optional computational logic |
|---|---|---|
| Addition, subtraction and multiplication | Average, namely Arithmetic mean | Sum, simple addition of different date's "Calculate another metric" data Weighted average, equal to average in this condition |
| Division | Weighted average The sum of "Return users' performance" across different dates / the sum of "Metric on Initial date" across different dates. | Sum, simple addition of different date's "Calculate another metric" data Average, Arithmetic mean of Sum |
# Influence of incomplete data on phase value
When phase value is computed, incomplete data will be ruled out. That is to say, the phase value is computed only based on complete data. You can use "[Exclude partial date]" to avoid misunderstanding. 
For example, if you view the phase value of retention rate between January 1 and January 7 on January 8, given the fact that the next day of January 7, that is, January 8, has not ended, the phase value is equal to the weighted mean of retention rates between January 1 and January 6, and the number of users involving the trigger action on January 7 and the number of users retained on the following day will not be included in the phase value.