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Logger Frequently Asked Question (FAQ)

Why doesn't a finger-stick calibration immediately and fully correct the reported Blood Glucose?

For expired mode, Logger mathematically tries to fit the line that fits the closest to the last 8 data points (meter finger checks) so it may not always correct exactly to your meter stick. The mathematical algorithm is based upon Least Squares Regression (LSR). Logger will not accept a meter bg if filtered and unfiltered values are more than 10% apart for safety reasons. There are at least two scenarios where filtered and unfiltered values can be more than 10% apart. First scenario is if blood glucose values are rising very fast or falling very fast. Second scenario is if the sensor is nearing the end of its life and becoming noisy/inaccurate. One other scenario is if the transmitter/sensor area is wet from pool/shower/sweat. You can check the CGM pill in Nightscout to see when the last calibration was accepted and used by Logger. Also, you may want to look at the Logger log file at the time of this calibration and tracing what Logger did with the calibration. Another file to check is /root/myopenaps/monitor/xdripjs/calibrations.csv which contains the current sensor unfiltered values vs. the corresponding finger-stick calibrations.