The range behind the numbers
Most CGM stats start from a range. Ando uses 70 to 180 mg/dL (3.9 to 10.0 mmol/L), the range many CGM reports use by default. It is the same everywhere in the app: on the home screen, on each workout, on each night and in the weekly wrap. One fixed range keeps your numbers comparable from one session or week to the next.
On Ando’s charts the line is green inside the range, amber above it and red below it. Need the range in the other unit? The glucose converter does it in one tap.
Time in range
Time in range (TIR) is the share of your readings that sit inside the range. If a workout has 24 readings and 18 of them are between 70 and 180 mg/dL, its time in range is 18 ÷ 24 = 75%.
Because a CGM reads at regular intervals, the share of readings is also the share of time: 75% of readings in range is 75% of the workout in range. Two companions follow from the same counting:
- Time below range: the share of readings under 70 mg/dL.
- Time above range: the share of readings over 180 mg/dL.
The three always add up to 100%.
Average glucose
The average is the plain mean of every reading in the window: add them up, divide by how many there are. It tells you where the line sat overall, but not how it got there. A flat line at 140 and a line that swings between 80 and 200 can share the same average, which is why the average is best read next to time in range and variability.
Variability (CV)
Variability answers the question the average can’t: how much does the line move? Ando shows it as the coefficient of variation (CV):
CV = standard deviation of the readings ÷ average of the readings × 100
The standard deviation measures how far readings typically sit from their average. Dividing by the average turns it into a percentage, so the swing is judged relative to where the line sits. For example, readings that average 140 mg/dL with a standard deviation of 42 mg/dL give a CV of 30%. The same 42 mg/dL around an average of 120 would give 35%.
| Example window | Average | Time in range | CV |
|---|---|---|---|
| Flat line around 140 | 140 mg/dL | 100% | Low |
| Gentle waves, 110 to 170 | 140 mg/dL | 100% | Moderate |
| Big swings, 70 to 210 | 140 mg/dL | About 70% | High |
Lows
In summaries such as the weekly wrap, Ando counts lows as episodes rather than readings. A low counts when glucose stays under 70 mg/dL (3.9 mmol/L) for at least 15 minutes. A new low only counts if it starts at least 30 minutes after the previous one ended, so one long dip is never counted twice.
Workout, night, week
The same numbers mean slightly different things depending on the window:
- A workout covers the activity itself, from start to finish, as recorded by your watch, Strava or health app. Ando shows the curve and the time in range and average for that window; the minimum and maximum appear on your Strava block and share cards.
- A night covers the sleep window from your watch or ring, with your sleep stages next to the line.
- A day and a week come together in the daily and weekly wraps: average, time in range, lows and variability, next to your workouts.
Why short windows swing
Short windows contain few readings. A Dexcom sensor reads every five minutes, so a 30-minute run has about six readings, and each one is worth about 17% of that run’s time in range. One reading just over 180 can move the number from 100% to 83%.
That’s normal arithmetic, not a sign that anything changed. For short sessions, the curve tells you more than the percentage. Over a night or a week, with hundreds of readings, the numbers settle down.
Keep in mind too that a CGM reads the fluid under your skin, a few minutes behind your blood. Our article on CGM delay explains why.
Ando shows these numbers to put your day in context. It doesn’t set goals for them or judge them. Targets for your own glucose are a conversation for your doctor.
Questions people ask
What is time in range on a CGM?
It is the share of your readings that fall inside a glucose range, usually 70 to 180 mg/dL (3.9 to 10.0 mmol/L). Because CGM readings come at regular intervals, the share of readings is also the share of time.
What range does Ando use?
Ando uses 70 to 180 mg/dL (3.9 to 10.0 mmol/L), the range many CGM reports use by default. It is the same range for every workout, night and week, so the numbers stay comparable.
How is glucose variability (CV) calculated?
CV, the coefficient of variation, is the standard deviation of your readings divided by their average, times 100. It describes how much the line swings around its average, as a percentage.
How does Ando count a low?
Ando counts a low when glucose stays under 70 mg/dL (3.9 mmol/L) for at least 15 minutes. A new low only counts if it starts at least 30 minutes after the previous one ended, so one long dip is not counted twice.
Can I change my target range in Ando?
Not today. Ando uses one fixed range everywhere. Targets for your own glucose are a conversation for your doctor; Ando’s job is to show what happened in context.