Companion App - Incorrect deltas / trend arrows and issues with the time it syncs

[petalina]

Discussed in #3784

^{Originally posted by petalina November 26, 2024}
Hello, since I switched from Dexcom One to Dexcom One+, using the Companion App as source, I have some issues with the arrows / difference of values and the time of update. I think somehow it is stuck in the time the older sensor used to update the values or something (eg some of the time points below - 1st pic: 8.47 / 103 mg/dl - 8.51 / 103 mg/dl - 8.56 / 103 mg/dl - 8.57 / 113 mg/dl, but delta: +41 mg/dl instead of 10 mg/dl) but I can't understand why the deltas it displays are so large even though the diagram and the values are correct. Also, at the same time the difference may be correct in the widget but with the wrong arrow (based on the real delta and xDrip's settings, not compared to the Dexcom app) and when I open the app both the arrow and difference are wrong.
I installed the latest version of xDrip+ yesterday and also tried to Restart Collector and restart my phone.

[Qxlkdr]

I can agree. I'm using xDrip+ since 2 days ago and loves it. Only using it as follower using my kids credentials to follow his Dexcom share (Dex Share).

Dexcom Follow is showing a "Falling slightly" arrow but xDrip+ is showing a straight down arrow:

At the same time, this is the result from the Home Assistant integration:

[overfrenk]

Same problem with eversense in companion mode, without companion mode the problem disappears! I could not solve the problem in any way.

[Navid200]

@Qxlkdr @overfrenk
The reason this issue was opened is the discrepancy between the difference between the last two xDrip readings and the xDrip delta value of 41 in the very first image in this thread.
If you look at that image, you can see that the difference between the last two readings is less than 41.

However, xDrip is not supposed to show the delta or the trend arrow that Dexcom app or any other app shows. xDrip is supposed to calculate the delta from the current and previous reading and calculate the arrow from that as well.
Dexcom app does not do that and uses a filer to come up with the arrow xDrip does not. We are not trying to present Dexcom app's arrow in xDrip.

If that is what you are interested in, you can open a discussion and we can talk about it.
Any other post in this issue that is not about the real issue it represents may be ignored.

[overfrenk]

The problem is the same, regardless of the BG source, just use companion mode! If you notice you will have several readings with intervals of 1 or 2 minutes instead of the classic 5 minutes. I also obviously have the trend arrow that shows badly and hallucinatory delta values ​​even at +/-50.

[Navid200]

@overfrenk Why would the timing impact delta? You would be right if xDrip showed the slope. But, it does not. It shows delta, which has nothing to do with the time axis. Why would we get a delta of 40 instead of 10, as explained clearly in the very first post of this issue, just because the readings arrive at a timing other than once every 5 minutes?

[petalina]

This observation about the time interval and the incorrect delta seems to be correct and it was a thought I quote from the initial discussion:
"Is there any chance that it uses the +10 md/dl delta in 1 minute (according to the time points but not the reality / Dexcom app) as 10 mg/dl/min and converts it to an "expected" +41 mg/dl in 4 extra minutes?"

The incorrect deltas are proportional to the 1 min. delta times ~4.

[Navid200]

@petalina Please forget the arrows for now.
xDrip calculates the arrows differently than Dexcom app. We have no plan to change that.

I asked this issue to be opened because I am not sure why there is an error in the delta.
If we address the delta, I will consider this closed.

With respect to the delta, how long does the error last?
I mean do you get this error for a few readings after you start a new sensor and then it goes away?

[petalina]

@Navid200 I didn't refer to the arrows in the last message but the incorrect deltas. The problem persisted for all the days the sensor lasted (10 days) though I changed back to Dexcom one to check what happens and there was no problem, the deltas are correct and a new value / point in the diagram is present every 5 minutes.

When I use the Dexcom one+, after a couple of times having a new value every 5 minutes, I get a new one 1 minute after the last; that's the pattern. Also, whether the last value is 1 or 5 minutes apart from the previous, the widget always has the right delta and simultaneously the app and the notification the incorrect. But the widget, while having the correct delta has incorrect arrow according to this delta and xDrip's settings (not considering the Dexcom app). If the interval between the values is 5 minutes, there's no issue with the app / notification as well, so maybe the time interval plays some role.

[overfrenk]

The "only in companion mode" problem of the delta and the arrow only happens with the readings strangely very close, normally they should be every 4/5 minutes but for some strange reason they randomly arrive at 1/2 minutes. Example with red circles. I repeat if I use the same "eversense" sensor with readings via xdrip and esel the problem disappears.

[FinnyChase]

It's pretty sad how dismissive Navid is about this issue. It's very clear from hundreds of forums that this trend arrow mismatch is a problem and not what the majority of people want. Wish they would at least add an option to just read the dexcom reading and arrow