I'd like to add the following to my original post (in actuality, it should replace my original post):
I've heard a lot of anecdotal evidence surrounding optimal times to calibrate, how often to calibrate, and when not to calibrate your Dexcom. A lot of the information I came across was conflictual, so I called Dexcom and was connected with one of their CDEs who, IMO, sounded like she knew what she was talking about; she did not sound like she was reading from a pre-scripted "Answers to FAQ" sheet. Following is a summary of the information she gave me. I make no guarantees regarding the accuracy of this information, so proceed with caution and with the knowledge that YDMV.
A. This is when you should calibrate:
1. When you are prompted to calibrate by either:
a. Two red blood drops that appear two hours after starting (or restarting) a sensor OR
b. One red blood drop (these prompts occur every 12 hours)
Caveat: Do not calibrate even if prompted to do so by a blood drop if the trend arrow is pointing either straight upwards or straight downwards (one or more arrows). If this is the case, WAIT until the directional arrow is either horizontal, trending slightly upward, or trending slightly downward before calibrating. Be patient; you will not be "timed out" if you do not calibrate immediately after a blood drop icon appears.
2. Whenever a meter reading is greater than or equal to 80 mg/dL AND the Dexcom reading is greater than 20% higher than the meter reading or more than 20% lower than the meter reading.
3. Whenever a meter reading is less than or equal to 79 mg/dL AND the Dexcom reading is more than 20 mg/dL (not 20%) higher than the meter reading or more than 20 mg/dL (not 20%) lower than the meter reading.
B. This is when you should not calibrate:
1. If BG (via meter) is higher than 400mg/dL.
2. If BG (via meter) is lower than 40 mg/dL.
3. If any of the following appear on the Dexcom screen:
a. question marks
b. an hourglass
c. the antenna icon (receiver is out of range of transmitter)
d. one or more trend arrows that point either straight up or straight down (horizontal arrow or arrows trending slightly upwards or slightly downwards are O.K.)
e. no trend arrow(s)
REMEMBER: More is NOT better when it comes to calibrating the Dexcom. Calibrating more often than when instructed to do so by blood drop icons or when the Dexcom reading is not inaccurate ("inaccurate" as defined by A.2. and A.3. above) will not improve the accuracy of your Dexcom and will likely worsen the accuracy of your Dexcom readings.
Some, but not all, of this information is available on the Dexcom website: http://www.dexcom.com/sites/dexcom.c...ney/story.html