Metrics center
Retention
Retention is not one grade. In Fluorgan, it is a reading of memory through two lenses: predicted estimates the chance of remembering now; observed shows what happened in recent qualified reviews.
Two lenses of memory
Predicted anticipates; observed checks. One does not replace the other because they answer different questions.
Memory changes over time
Even without reviewing, prediction can fall because time passed. That does not create an observed error; it creates a lower current estimate.
Predicted vs observed
Divergence can suggest an optimistic model, small sample, recent difficulty, or a real change in the material. A prudent reading preserves that uncertainty.
Explore an example
An educational example with 12 cards shows memory state, time passing, valid review, and recovery without inflating the numerator.
What counts as a valid review
The first primary, due attempt in a consolidated phase enters the contract. Learning, same-cycle recovery, not-due Safe Ahead, variant, pretest, contrast, and probes stay out of this metric without losing operational value.
How we calculate
Current predicted retention consumes the public contract formula; observed consumes successes over qualified reviews; Retention Over Time uses historical prediction persisted before the answer.
Evidence changes the reading
The same raw percentage can carry different weight. Missing evidence is not zero, and a technical error is not empty.
How to interpret combinations
High/low in this block is only a synthetic teaching scenario. The page creates no new thresholds.
What Retention does not measure
Retention does not measure content that never became cards, complete understanding, transfer to a new context, exam performance, approval, or absolute card quality.
How it appears in Fluorgan
The simplified representation shows where value, predicted/observed lens, trend, evidence, and interpretation path appear in the Progress surface.
Contract and review
Public details show contract version, policy, window, timezone, states, population, and last review without exposing SQL or unnecessary internal names.