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Extract Values from html via HTML parser

I initially asked about a way to grep/awk.....directly from an HTML file....I got some feedback but first I see that people did not have the whole HTML and so the solutions failed.... now some mentioned that html parsing would be much better option....as I have no idea i kindly would like to ask the experts here how this would work and if easily possible provide some input....I work on raspberry pi with standard linux/debian wheezy.

the html mentioned is found here, simple html...but guess important to see the whole file to be able to help:

https://www.dropbox.com/s/9jdgzen2hwjxhjp/main.htm

So what is required is to extract the two values.....Pplus and Pminus (18.0000 and 0.00000) and provide them, plus providing the SUM.... both values come from a smart meter (energy meter) that provides the energy generated P- and energy/power taken from the network P+......P- in case of sun and solar plant working...so 18W is at night...0.0000 means no generation as no sun....just to give you some background information.

I tried to update and ask for support in the original threat but seems that nobody does see it again as for days now no feedback....this is my attempt now to bring this back to the experts here in the forum. Thanks a lot Norbert