In reply to Alison Turnock.
The chart is not directly comparing device type usage in traffic terms. It looks at how different types are used through a day. So about 8% of tablet accesses take place 8-9pm while just 4% of desktop accesses happen then. 100% comes from summing hourly accesses for a particular device.
Desktops are still dominate in getting users to the site, but I'm looking at how devices get used through the day.
Yes, the chart could have been clearer.