Focus Vs Concentration: Why Sarenica Tracks Both
Concentration tells you what is happening in the next minute. Focus tells you what happened across the last block. They look the same in the abstract and behave nothing alike in the data.
The single-word problem
In casual use, focus and concentration mean the same thing. In tracking data they behave nothing alike, and conflating them is one of the easier ways to misread a report.
Sarenica records both because they answer different questions. Concentration answers "what is happening right now in this minute". Focus answers "what kind of block was this".
Concentration: what the camera reads moment-to-moment
Concentration is a per-minute score derived mostly from camera signals: gaze direction, blink pattern, micro-movements, and head-pose stability. It moves fast. A good minute can climb to 80, a distracted minute can drop to 20, all within the same hour.
It is not a verdict on the session. It is a snapshot. That is why the live readout in the desktop app shows concentration but a daily summary tends to lead with focus.
Focus: the sustained pattern
Focus is computed across a window of minutes, not a single minute. It captures continuity: how often the per-minute concentration stayed in a usable range, how stable the head-pose was over time, how much of the session was spent in genuinely engaged work versus low-engagement passive presence.
A minute can spike to perfect concentration and the focus score for that session can still be mediocre, because focus is sensitive to the gaps between the spikes. That is exactly the property that makes it the right signal for "was this a good block".
Why a high concentration moment does not mean a focused hour
Almost everyone has high-concentration minutes scattered through bad sessions. The brain locks in for 90 seconds, then drifts, then locks in again. That is normal.
Focus is what filters out the spikes. If you have 12 high-concentration minutes spread across 60 minutes of a fragmented session, focus will be low even though concentration looked great in moments.
The reverse is also true: a long, steady, slightly less intense session can score lower on peak concentration but higher on focus, because the continuity is what matters.
How they show up in your weekly report
Weekly progress reports lean almost entirely on focus, because the question is "what kind of work blocks are working for me". Concentration shows up underneath, mostly as input into focus and as one of the per-minute signals feeding fatigue burden.
If a report finding says "30-45 minute sessions show lower focus", what it usually means is the late minutes of those sessions stopped sustaining concentration, not that you were never focused at all. Same data; different lens.