How do I calibrate my sensor?

When is a finger stick calibration helpful?

In general, the Signos system is designed to work properly without calibrations. Your body responds slightly differently to each sensor. This means you can have sensors baseline at different levels, as one may baseline at 85 and the next one could baseline at 95. It is best to look at the relative spikes to food, stress, sleep, and exercise versus the absolute numbers.

However, finger stick calibrations can be helpful to help maintain a consistent baseline across sensors. A finger stick calibration may also be helpful if the glucose number you are seeing seems significantly different than it should be. 

Finger Stick Comparison Best Practices

If you are comparing the readings between a glucometer and a CGM, please only do so when your glucose levels are stable. This would be either first thing in the morning or 2-3 hours after a meal or exercise. 

This is because the CGM is measuring the glucose in your interstitial fluid—the fluid that surrounds the cells of your tissue under your skin—while the glucometer is measuring blood glucose. Glucose moves from your blood vessels and capillaries first and then into your interstitial fluid. This means that the CGM readings can lag behind blood glucose by up to 15 minutes.

You can read more about comparing CGM readings with finger sticks here.

Accuracy: The 20/20 Rule of a CGM

The Dexcom G7 CGM has a MARD (error rate) of 8.2% and the data follows the %20/20 Rule when comparing readings with blood glucometers, which have similar error rates of their own. Dexcom calls it the 20 Rule. To be considered a close match, the Dexcom reading must be within:

• 20% of the meter value when the meter value is 80 mg/dL or higher
• 20 mg/dL of the meter value when the meter value is under 80 mg/dL

For example, if your glucose meter reading is 100 mg/dL, your reading is a close match if it’s between 80 and 120 mg/dL.

How to Calibrate

The Dexcom G7 allows users to calibrate the sensor readings with a value they believe is closer to accurate, like one from a glucometer. 

The G7 may accept or reject any calibration value in order to maintain accurate readings. Values that are most likely to be rejected are those far from the current reading or those entered within the first 24 hours.

To calibrate your sensor, follow these steps: 

1. When your glucose is stable, take a comparison reading
2. In Signos, go to Settings > CGM > Calibrate Sensor > enter the value
3. Your readings will begin to adjust to the new calibration over the next several hours