With regards calibrating proximity sensor tool can be found in the settings. Scroll down to the very bottom and select “Maintainance”. Then choose “Proximity sensor”.
Battery first charge, see here: https://support.fairphone.com/hc/en-us/articles/207891033-How-can-I-charge-my-Fairphone-2-
If device discharging quickly see here: https://forum.fairphone.com/t/pencil2-a-little-guide-to-fairphones-batteries-fp1-fp2/5618
Extending battery life: https://support.fairphone.com/hc/en-us/articles/115001847943-Extend-the-battery-life-of-your-Fairphone
You could look at ContactSync: http://ntbab.dyndns.org/apache2-default/seite/contactsync.html and CalendarSync:http://ntbab.dyndns.org/apache2-default/seite/icalparseandroid.html which can be used independently of Google.
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