Cwa-app-ios: Weird variations/spikes in match count on iPhone 12 Pro

[holicodes]

Technical details

• Device name: iPhone 12 Pro
• iOS Version: 14.2.1
• App Version: 1.7.1 (0)

Describe the bug

First of all, thank y'all for contributing to this software – the code and the discussions here are a beautiful balance to the madness outside.

To my point: I see strange spikes in my green encounters and I feel like it could be related to switching from an iPhone 8 Plus to the new iPhone 12 Pro.

Today, I have 10 low-risk matches whereas my girlfriend only has 5 on her iPhone Xs. I don't use public transport, work from home and only go out for groceries, almost always together with her. We live in a big city in Germany.

I started taking notes on November 19, exactly 2 weeks after setting up the new iPhone, to have more than the 14-day view of the iOS logs. Earlier than Nov 19 (also on the old phone of course), I never exceeded 3 matches but I know that we had infection numbers rising a lot during that timeframe. Here's what my notes look like:

Date | Match count
------------ | -------------
Before | never more than 3
Nov 19 | 5
Nov 20 | 8
Nov 21 | 11
Nov 22 | 3
Nov 23-25 | 2
Nov 26 | 1
Nov 27-30 | 0
Dec 1-2 | 0
Dec 3-7 | 1
Dec 8 | 1 at 16:01, 9 at 20:02 CET
Dec 9 | 9 at 08:05, 10 at 12:06 CET
Dec 10-11 | 10

During this time, my girlfriend never had more than half of my matches and she even used public transport a couple times whereas I didn't.

Do you think this could be in any kind related to the new device and its Bluetooth performance or is it likely to be pure coincidence that my phone simply cast more (later positive) IDs?

Expected behaviour

With infections being at a fairly consistent level, I can't explain why my matches are not. Besides, it irritates me that I have so many more matches than

Additional context

As a control device, my work phone (iPhone Xs) shows zero matches so I can exclude any impact from the surroundings/neighbours of our flat. Exposure log is attached.

ExposureChecks-2020-12-11.txt

[Ein-Tim]

See also #1531

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@thomasaugsten stated here:

This is already normalised by apple to have comparable attenuation between the devices

But as you can see @holicodes, you are not the only one who notes that CWA shows more encounters on your iPhone 12 then it showed on the old iPhone.

I think the (very simple) answer to the question why this happens is that the iPhone 12 definitely has better BLE hardware and so records more encounters. The normalisation put in place by Apple seems to work not that good...

[holicodes]

Thank you @Ein-Tim for the quick reply! And shame on me for not finding this one earlier, looks like a duplicate indeed.

[Ein-Tim]

@holicodes
No problem. As the author of this Issue you can go ahead and close it 👍

I think it would be helpful to have your information in #1531.
So if you like to, you can follow up there.

Have a nice weekend and stay safe!

[wolfgang35435]

Yes, after upgrading, my green count went from 3 to zero. Apparently there was a calibration problem with the new devices.
Have a nice and safe Christmas.