stevieb hippo marto and Hauke D, Thanks so much. I hope I will be able to help others one day too, if not by my knowledge, then by some experience in my future projects I expect will have

I will answer to all replies soon, but first just to add few comments to my main post.

Regarding data frequency it should be 3 or 4 times instead of 2, because not all measurement will be done at the same time, but that doesn't matter much. It is also possible for some data to be held for some time and then to send few data together. For my purposes, it is not so important to have all data immediately on the server

In meantime, after sending my post yesterday, I've got one maybe a bit strange or even ridiculous idea (I still don't have a right sense of that) about situation with many locations for monitoring

I could send SMS messages from PIC or some other monitoring devices to a small server that I should have in that case, in my home or some other place with internet connection. I don't have many data during the day, so there would not be so much messages. On the other side I think SMS messaging sometimes may be late or unsure, so that idea is maybe not recommended.

Regarding representing graphs for longer time then for one month, I've got an simple idea. I would plot one graph in a month and when next month comes, its graph will be shown on the HTML page instead of previous, and other graphs in server directory would have links on that page, so visitor could choose what they want. I see now there are numerous options

Kind regards

predrag