Uploading incorrect delta to Nightscout

[cascer1]

Originally created as nightscout/cgm-remote-monitor#4693

Describe the bug
The delta reported by the nightscout API (for example /api/v1/entries/current.json) is different from the actual BG delta. According to @sulkaharo this is caused by xDrip uploading incorrect deltas to Nightscout.

To Reproduce

1. Observe delta reported by xDrip (in the xDrip app)
2. Calculate actual delta (using last two readings, should be the same as xDrip)
3. Observe delta reported by Nightscout (not API, should also be the same as xDrip)
4. Observe delta reported by API (this is often different)

Expected behavior
The BG delta uploaded to Nightscout should be the actual delta.

Screenshots
Recording displaying discrepancy

Your setup information

• Nightscout version 0.11.2-rc2-20190323
• xDrip nightly 20190530-a25cacb
• Dexcom G6

Additional information
This issue never occurred for me when I was using a Dexcom G5.

[dmelliott20]

did you get to the bottom of this. I'm experiencing the same issue

[cascer1]

I bought a new phone that doesn't work well with xDrip so i switched to another app.

[Navid200]

@cascer1

Observe delta reported by Nightscout (not API, should also be the same as xDrip)

Where is this delta, which is correct, coming from if not from xDrip?

[Navid200]

I can recreate this problem. So, I will see if I can understand more about it and hopefully fix it.

But, the problem seems to be, at least for me, directly related to the problem reported here: #691

If there is a reason this is a different matter, please explain and help me understand and I will reopen this.
Thanks for reporting.