For the Dexcom G6 CGM: After entering the sensor code, you do not have to calibrate.
For the Dexcom G5 Mobile CGM: You must enter two calibrations (aka “double blood drop” or DBD) after the two-hour warm-up period. Both of these calibrations should be done on the same device.
After the initial DBD, you will need to calibrate once every 12 hours for the full lifespan of the sensor session (seven days) and this can be done on either device.
Important note about Dexcom support:
Dexcom and Tandem have agreed which system issues are best handled by each company, including which company is responsible for reporting those events to the appropriate regulatory authority. To help ensure that the required reporting takes place in a timely fashion, customers may need to contact Dexcom for some issues and Tandem for others.
Tandem handles issues with the connection between your Dexcom transmitter and t:slim X2 pump, questions about calibration, the “---” display, and sensor failures after the 2-hour warmup period.
For all other CGM issues, including the sensor failure during the 2-hour warmup, “no restarts” alert or physical problems with your sensor or transmitter, such as bleeding, bruising, skin reaction, adhesive issues, applicator issues, or broken wires, you should contact Dexcom using one of the options at dexcom.com/contact.