Medical sources

Time in Range

The percentage of CGM readings between 70 and 180 mg/dL (3.9–10.0 mmol/L). Readings below 70 mg/dL count as low and readings above 180 mg/dL count as high, so in range, low and high always add up to 100%. The Time in Range cards, the daily bars and the trend chart all use this same band.

This is the standard band from the International Consensus on Time in Range. For most adults with type 1 or type 2 diabetes it suggests aiming for more than 70% of readings in range, under 4% below 70 mg/dL and under 1% below 54 mg/dL (3.0 mmol/L). Targets are different in pregnancy and for older or higher-risk adults, and your care team may set different ones for you.

Time in Range always uses this fixed band, even if the target range on your Nightscout site is different. Your own target range is what colours the glucose chart.

The consensus recommends judging these figures over at least 14 days with the sensor worn about 70% of the time. A single day, or the first few days of a month, can look very different from your longer-term picture. A day with fewer than about 6 hours of readings shows as a grey bar rather than a percentage.

Estimated A1C (GMI)

Calculated from your average CGM glucose with the Glucose Management Indicator (GMI) formula. The month card uses every reading since the 1st of the month; the trend chart uses one week at a time.

GMI estimates the A1C a laboratory test might report, but it is not a lab result and the two can differ. Its authors note that 10–14 days of CGM data give a good estimate, so early in the month the figure rests on only a few days.

GMI (%) = 3.31 + 0.02392 × average glucose in mg/dL

Glucose variability (CV)

The coefficient of variation: how widely your readings swing around their average, expressed as a percentage of the average. Lower means steadier glucose.

The international consensus on CGM defines a CV below 36% as stable and 36% or more as unstable, and the Time in Range consensus lists 36% or less as the target.

CV (%) = standard deviation of readings ÷ average glucose × 100

Low events

A low event starts when readings stay below 70 mg/dL (3.9 mmol/L) for at least 15 minutes, and ends once readings are back at or above 70 mg/dL for 15 minutes, so a brief bounce back up does not split one low into two. This follows the event definition in the international consensus on CGM.

If the sensor sends no readings for more than 30 minutes, an event in progress ends there, because the app cannot know what happened during the gap.

Insulin on board, carbs on board and recommended bolus

When your Nightscout site reports insulin on board (IOB), carbs on board (COB) or a recommended bolus from Loop or a similar system, Aura T1D shows that system’s own figures unchanged. It does not recalculate them, and it never calculates doses.

If no figure is reported, the app shows a simple estimate instead, and the curve on the Active Carbs chart always uses it: each bolus counts down in a straight line to zero over 4 hours, and each carb entry over 3 hours. This is a rough display aid defined by Aura T1D, not a clinical formula. How long insulin keeps working varies by person and insulin type, and there is no single agreed value for it. Never use this estimate to decide a dose.

Total daily dose

Boluses plus basal for each full day, added up from what your Nightscout site recorded. Basal is estimated from the rates your loop reported each hour, and a day without enough loop data shows no total. It is a record of what was delivered, not a recommendation, and is only as complete as the data uploaded to your site.

This week’s insight

Picks one pattern from the last 7 days: a time of day when lows or highs keep happening, a day that stood out, or your steadiest stretch. It uses the target range from your own Nightscout settings (70–180 mg/dL if none is set). A stretch counts as your steadiest only at 70% or more in range, the goal suggested by the Time in Range consensus.

Insights point out patterns worth discussing with your care team. They are educational, not medical advice.

Trend line on the chart

The dashed line continues the direction of the last 30 minutes of readings for up to an hour, flattening as it goes. It is a drawing aid defined by Aura T1D, not a prediction from a clinical model. Glucose can change direction at any time.

Alert levels

Urgent low and urgent high alerts use the levels set on your Nightscout site. On a Dexcom account they use the app’s standard levels: 55 mg/dL (3.1 mmol/L) and 260 mg/dL (14.4 mmol/L).

For reference, the consensus classes glucose below 54 mg/dL (3.0 mmol/L) as a clinically significant (level 2) low and above 250 mg/dL (13.9 mmol/L) as a level 2 high. Alerts are a convenience and do not replace the alarms in your CGM app.

References

1. [1] Battelino T, Danne T, Bergenstal RM, et al. Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range. Diabetes Care. 2019;42(8):1593–1603. doi:10.2337/dci19-0028 · Free full text
2. [2] Bergenstal RM, Beck RW, Close KL, et al. Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring. Diabetes Care. 2018;41(11):2275–2280. doi:10.2337/dc18-1581 · Free full text
3. [3] Danne T, Nimri R, Battelino T, et al. International Consensus on Use of Continuous Glucose Monitoring. Diabetes Care. 2017;40(12):1631–1640. doi:10.2337/dc17-1600 · Free full text
4. [4] Walsh J, Roberts R, Heinemann L. Confusion Regarding Duration of Insulin Action: A Potential Source for Major Insulin Dose Errors by Bolus Calculators. J Diabetes Sci Technol. 2014;8(1):170–178. doi:10.1177/1932296813514319 · Free full text