Dexcom G6 arrows seem strange at times

Does anyone wonder why the Dexcom arrows seem to behave strangely at times? I’ve gotten a half-down arrow on a reading that was actually higher than the prior reading and double-down arrows followed immediately by sideways arrows. It seems these indicators can at times be a little misleading and perhaps lead to improper bolusing.

Yeah, I’ve watched that happen and have learned that any significant treatment moves should be confirmed with a finger-stick. I’ve been burned on this more than once.

My numeracy is fairly good and I sometimes wish I could talk to a Dexcom algorithm insider when this happens. Here’s an example of a “conversation” I’ve had with my CGM:

CGM: 50mg/dL
me: w/ fingerstick data: 75 mg/dL
CGM: 51 mg/dL
me: w/ fingerstick data 15 mins. later: 74 mg/dL
CGM: 49 mg/dL (Argh! What an idiot!)

The only thing I can conclude from this is that the electrical signal coming from the sensor tip is given much stronger weight in the calibration scenario than we sometimes think it should. I interpret this kind of thing as an indication that the sensor is failing and I should replace it sooner rather than later.

But sometimes the calibration works and the sensor turns into a star performer. It baffles me!


I have had doubts about arrow integrity.

I think sometimes it doesn’t match up because the software adjusts numbers to (what seems like) smooth out the curve. My Dexcom app gives me one thing, but my watch (Pebble, getting data from Clarity) is slightly behind so I can see when it actually changes the numbers a bit. That’s my guess - may not answer your question, but something I’ve noticed!

I do see odd arrows, but only occasionally. I may not be paying close enough attention, but when I see it, I have rationalized it as the arrows waiting for more data before changing. Like, Caleb’s been dropping, but a reading went up - arrow is still downward until it determines the upward direction is continuing. Maybe I’m giving it too much credit?

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I had an odd experience the other evening. My G6 warned me that I was going low and that I would be at 55 mg/dL within 20 minutes, so I ate some food. Basal-IQ had shut off pump delivery.
I kept monitoring my BG on my phone. My wife uses the Dexcom Follow app, so when my BG reached 58, I warned her that I was heading low (but I had already eaten!), and she might get an alarm. She opened the Follow app on her phone, and it also read 58, but the Dexcom app on my phone had a Slowly Falling downward arrow, while the Follow app on her phone had a Steady horizontal arrow.
WTF? They are both getting the same data, but giving different arrows.
BTW, looking at the graph on my phone, I think the Steady horizontal arrow was much more appropriate.

Like Terry4, I sometimes wish I could talk to a Dexcom algorithm insider.

Maybe a future Dex version will have a voice response capability and we could ask, “Hey Al(gorithm), what are you thinking here?” and the response would be in the voice of Hal from 2001: a Space Odyssey …

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This one from that movie fits:

HAL 9000: I know I’ve made some very poor decisions recently, but I can give you my complete assurance that my work will be back to normal. I’ve still got the greatest enthusiasm and confidence in the mission. And I want to help you.

Or even this one:

HAL 9000: This mission is too important for me to allow you to jeopardize it.

This could lead, however, to some cathartic Dexcom equipment smashing!


That is exactly what is happening. At least in the scenario you describe.

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When I first switched from the G5 to the G6, I was exasperated by impossible and inconsistent arrows. As time has gone on, I’ve come to trust my G6 more.
I think it is definitely a good idea, if you can, to wait a few cycles before reacting forcefully to what the Dexcom arrows are saying. For example, I’ve given myself large boluses in response to double up arrows only to have the following reading be a steady horizontal arrow. Or, on the other side, I’ve eaten in response to a double down arrow on a blood sugar that wasn’t low but seemed to be heading low fast only to see it level out before the food I’d eaten would have had any chance to be absorbed.
Arrows or no, I’m trying to become a little more patient and to let things develop a bit rather than taking actions or checking the Dexcom against a finger stick. Obviously, if your reading is low, you don’t have the luxury of the wait and see approach



I eat a banana every morning for non-D health reasons, and I have learned that I need to be careful of overreacting to the double up arrows that happen every so often, because in 15 minutes the arrow will go to the right and my BG will slowly start trending lower.

Hehehe, they probably don’t have the answer either. Such is the nature of software (especially malfunctioning software).

We pay far more attention to the dots and how the line is forming than the arrows. The arrows predict based on the last three readings, which is not so useful a lot of the time.

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