This graph shows live temperature data from my house. The blue line is the outdoor temperature, measured from a thermometer on my front porch. The black line is the temperature in my office upstairs, and the red line is from the living room downstairs. The green line is the latest forecast for outdoor temperature from the National Weather Service's National Digital Forecast Database.
The graph uses Multigraph and is interactive; you can click and drag the mouse to see other parts of the graph. Hold the SHIFT key down to zoom in or out while dragging. The data will move along whichever axis is highlighted; pass the mouse over an axis to highlight it.
As you move around to expose new parts of the timeline, the graph uses a web service to fetch more data from a database. The database contains data going back to early 2008.
The data in these graphs is from a series of "1-wire" sensors that are connected to a computer that records the sensor values every 5 minutes and uploads them to this web site.