How this graph is generated
I have installed a small temperature sensor on my balcony and connected it to my Raspberry Pi. A Python program takes a temperature reading every 10 minutes. The values are stored, along with the times, in a log file and with matplotlib the graph is created from the log file. The graph is then stored in a directory on the web server and can be accessed through the internet.
From the morning until the early afternoon the graph can look rather jagged. This is due to the fact that the sun shines directly onto the sensor (if it shines at all) with passing clouds casting a shadow on it occasionally. After about 2 pm the sun has gone around to the other side of the house and the graph becomes a little smoother.