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:
For "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.
If you have paired a Dexcom CGM with your Tandem insulin pump, and your question isn't answered in this help section, you should contact Tandem customer technical support for all other issues by calling (877) 801-6901.