You’re right Ally,

this afternoon I thought about extra option, which I’d like to bring in:

What if the primary uradmonitor-url is fixed and second an third could be manually set (by the user over local webserver) or by requesting an extra information on uradmonitor once a day.

Maybe
1) Fixed uradmonitor.com
2) Variable request from uradmonitor.com (one of the volunteers you said)
3) Also variable request from uradmonitor.com
4) Variable in users choice (don’t know, if necessary and whished by you).

The synchronisation bings the need of transmitting also the timestamp.
In my personal implementation this is optional possible at the moment. But with this you can absolutely disturb data in the database.
Currently you only can disturb current values.