If you don't want to write code to use our API then the other way to accomplish getting a value to a webpage would be to create a Graphical View
You can read about this in our wiki http://infiniteautomation.com/wiki/doku.php?id=graphics:mango_graphic_views:editing_graphical_views
Once you have the graphical view working you could display that on your custom html page in an iframe. Here's a link explaining how to use iframes
Sorry I didn't understand.
OK I think this will help you.
In Mango click on Custom Dashboards on the main icon menu at top of the page. Here you will see many examples. Here's a video as well
By The Way - You can do a view source in your browser to see the html for these examples or goto <mango root dir>/web/modules/dashboards/web/private