Dexcom G5 Calibrations

I’m comparing Dexcom readings (using Dexcom receiver) and Xdrip readings (using Phone and Native not checked) at the same time. Readings are being compared to Contour Next meter which I have found to be very accurate. Have about 50 readings so far.

Dexcom states you should calibrate the G5 every 12 hours. For this comparison, I am calibrating my receiver every 12 hours and I am calibrating my phone (Xdrip app running with Native unchecked) only when readings are very inaccurate.

Which would give me a better comparisons for this test?
1- Calibrate receiver every 12 hours and phone when its readings are very inaccurate? What I am currently doing.
2- Calibrate both receiver and phone every 12 hours?
3- something else?

Any advice?


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I suggest to take the “every 12 hours” with a grain of salt.

Or a pound of salt.

The nag screen will come up on the new G5 touchscreen receiver 12 hours after the most recent calibration however it is nag only and you will still get your BG readings.

IMHO it is MUCH more important to choose carefully the time to calibrate based on what the BG is doing.

Calibrating when the BG is anything OTHER than straight and level is more likely than not IMHO to impact the accuracy and degrade the data you get.

When we were on the G5 we would typically calibrate for the first two days and then just stop. Check against a meter sure. But if close than we would not add more calibrations.


I just noticed said about calibrating different devices.

That is NOT how the G5 operates. That was how the G4 worked but the calibration approach is different with the G5.

With the G5 (and G6 if you are calibrating) the calibrations are not stored in the receiver or phone but rather are sent to the transmitter and stored in the transmitter regardless of what device you use to enter the calibration.

This means if you are entering a calibration you DEFINITELY DO NOT WANT to double enter the calibration in both the phone and receiver. This will not do what you want. The transmitter will see this as a double calibration.

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Thanks Thomas.

So if I am calibrating the receiver then the phone picks it up as a calibration even through I an not using Native on the Xdrip app on the phone.

So is your recommendation that I only calibrate (on either the receiver
or the phone) if the reading are significantly inaccurate? I don’t calibrate until the arrow indicates stable. Should I calibrate on either the phone or Receiver depending on the device that is most inaccurate?

Apparently they are both accepting raw data but are giving me different readings because of their algorithms. What causes the raw data to go haywire at times? I see this when they both change by a ridiculous amount at the same time, I know it is wrong and then they start correcting without a calibration.

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Anything xdrip I have no experience.

Whatever @docslotnick says.

@RCA221 If you don’t use native mode in xDrip+ the calibrations won’t be taken from the transmitter. XDrip+ only uses a snippet of the data on each data burst from the transmitter. Native mode tells xDrip+ to take the whole data burst.

If you’re doing a comparison I would suggest that you calibrate both at the same time (from a single finger stick, so it’s the same number) otherwise you are causing the algorithms to be different, not your blood sugar.

Your experiment has been done before, and different people get different results. This is truly one of those YDMV moments.

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@Thomas XDrip+ in regular mode has one way communication (transmitter to receiving device, phone or watch). In native mode it’s two way (collector to transmitter and transmitter to collector)

So in non native mode xDrip+ has no idea of a calibration on the Dexcom receiver, and the transmitter also is not informed of the calibration in xDrip+.


I am gradually get up to speed on the complexities of Xdrip thanks to you.

So is the whole burst of data better than a snipped of the data which would argue for native made, I think. I understand that I could simultaneously calibrate both with the same blood from my Contour next. I understand that would make things more comparable. That is probably the test I should do.

But assuming non-native comes out the best, which I am hoping for. I would then use non-native. If I do, what is your opinion of then calibrating 2x a day versus calibrating only when there is a significant change with the Contour Next?

Which do you use, native or non-native?


@RCA221 Native mode gets the exact same data as the Dexcom receiver or app. No difference. So that would make testing the two against each other pointless–they will always be the same (except you may notice a few seconds lag in xDrip+ displaying the reading). In Native mode the algorithm is in the transmitter.

I use Native mode because I need to use the Dexcom receiver for Medicare compliance.

If using non -Native mode I would probably still calibrate the G5 twice a day. The G6, never.

And if things go haywire with the algorithm and you’re consistently getting disparate readings between xDrip+ and the Contour, you can always delete your calibrations and start the sensor over again.

I am on Medicare. I thought that was a rule years ago but not anymore. Tons of people on Medicare use their phone and not their receiver. Have never been asked about it by anyone.

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@RCA221 When I signed up for a Dexcom paid for by Medicare (just about a year ago) I recall I had to agree to some terms, which included using a receiver for most of the readings.

Has this changed?

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@Thomas So CMS has gotten some common sense. Thanks for the link, I’m surprised I haven’t seen this before.


After 2+ weeks I just inserted a new sensor. As you know I do not have Native checked. I expected that I would not have to wait 2 hours before seeing new readings. But my screen says “Please wait while sensor warms up (94 minutes).” What did I do wrong?

@RCA221 There is still a 2 hour warm-up in xDrip+. You should see readings on your watch but they will be highly inaccurate.

You can speed up the 2 hours by adding a calibration about once every half hour. But I would just chill and wait for the 2 hours.

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I still have to wait 2 hrs even if I am not on Native? So that is only when you truly put in a new sensor? In non-Native I still don’t have to worry about restarts? Am i correct. Sorry I thought I was way beyond this but it truly surprised me that I had to wait 2-hr for stop and start. By the way I have soaked the senor for about 20 hrs so I expect that to cut down on the inaccuracies.

Another surprise I just found out about today. I looked at the BG Table and the numbers were not the same as I had seen on the screen for about the same times. I suspect when you calibrate, the BG table goes back and changes data based on the new calibration. Don’t think I explained that well. Do you know anything about that?

@RCA221 Yes, you only have to go through a 2 hour warm-up on a new sensor start. You do not need to do anything until the sensor dies. This is on G5.

Actually, soaking for so long will only shorten the useful life of the sensor. It probably doesn’t have much effect on the accuracy of the sensor. The 2 hour warm-up should be a sufficient soak.

There is a setting called “rewrite history”. If it is checked the glucose numbers will change based on calibrations.

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Thanks, with this information I think I can now run Xdrip well. (Or now be dangerous to myself :.)

Thanks for all your help. Sorry for all the impositions. Been a T1D for over 50 years and now have a ave bg of 105 and std dev of <20. Now that I am retired, my hobby is better management of my diabetes. Latest attempt is to see if Xdrip can be part of my daily routine. I think it can. Please feel free to message me on anything relating to diabetes.



@RCA221 That is quite an impressive ave. Bg and a phenomenal SD! I’m also retired and have also taken up diabetes as somewhat of a hobby, but my average is about 115 with SD of 35. (Can’t seem to get that SD down).

I’ve been diabetic for 48 years, and can tell you that Dexcom hardware and xDrip+ software are truly miracles!

Glad I could help you a little bit! And it’s never an imposition.

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I tried but couldn’t find this setting. I’m looking to uncheck it.