Lesson 06 · 4 min · 6 things to do
Signals worth reading
Tell apart a measurement that carries information and one that carries noise.
You measure your resting heart rate on one morning and it is higher than usual. What have you learned?
- Yes.Any measurement varies from day to day for reasons that have nothing to do with what you are watching. The information is in the pattern across many days, and one point has no pattern.
- Not quite.It might mean that. It might also be the room temperature, the time you woke, or a coffee — and one number cannot separate them.
- Not quite.It becomes meaningful once it joins a run of readings. The mistake is reading one point, not taking readings.
One reading is noise with a number on it. A signal is a run of readings you can compare against your own usual range.
The same daily measurement, read over different windows.
One dayTwo weeksThree monthsThis morning58 bpmYesterday morning55 bpmthe only other reading you have
One dayTwo numbers, three beats apart. Higher or lower than what?
This morning58 bpmYour two-week average56 bpmTwo weeksA range appears — 52 to 60 — and today sits comfortably inside it.
Average three months ago52 bpmAverage now56 bpmThree monthsThe average itself has moved from 52 to 56. That drift is the finding, and no single morning contained it.
Which frame contains information you could act on?
- Yes.Trends survive the noise that swamps single readings. It is also why they are the least satisfying thing to look at: they only appear after weeks of readings that each said nothing.
- Not quite.Most current and least interpretable. Currency is not information.
- Not quite.Useful for spotting an outlier. It cannot see the drift, because the range moved with it.
Move the control to see what changes.
Which of these carry information about how a body is coping, and which mostly carry noise?
A three-month trend in resting heart rate.
Whether you woke before the alarm, on one morning.
How many nights this month you slept badly.
A single day's step count.
Whether the same task feels harder than it did in spring.
Yes.Everything in the left column is a count or a trend over time. Everything in the right is a single sample of something that naturally varies — which is what most devices show you most prominently.A device gives a daily "readiness score" out of 100. What should you know before using it?
- Yes.The inputs are usually a handful of ordinary measurements; the weighting is a choice made by the manufacturer. A score can be genuinely useful and it is not a measurement of anything in itself.
- Not quite.Worth knowing, and it does not tell you what the number means on a given morning.
- Not quite.A number that combines several things in an unstated way cannot be checked against anything, including itself.
Your resting heart rate normally sits between 52 and 60. Over the last ten mornings, six readings were above 60. Roughly what percentage of readings left your usual range?
%Yes.Six out of ten. It is the count outside the range that carries the signal — the individual numbers are the same kind of measurement that told you nothing on day one.What makes a measurement worth taking at all?
- Yes.Both halves are needed. A measurement that never moves tells you nothing, and one that moves for a dozen unrelated reasons tells you nothing either.
- Not quite.Ease is why most collected measurements exist, and it says nothing about whether they carry information.
- Not quite.Precision is how finely it is reported. A precisely measured number that varies for six reasons is precisely uninformative.
Lesson complete
One reading is noise with a number on it. A trend is a signal.
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