I had a look at the site. The way it is written, the website refreshes at a given rate set with a METATAG. This you cannot change.
However, everytime you hit the refresh button on your browser you will see the latest read out from their unit, it appears to be a constant dataflow as you can refresh in less than 2 seconds and you have a change in the reading.
Due to this I doubt that they store the data in a database as this would create a huge one within a very short time.
If they are so friendly to allow you to copy their data to your website, why not approach them again and ask the one who programmed the site...he can give you the exact code for that particular element you want, also I doubt he will allow you access "behind" the doors as this will open their server and make it vulnerable to attacks...
Perhaps you see now why I tried to warn you about this idea.