How accurate is Seattle City Light’s daily usage graph?

When I log onto the SCL portal they have an option to view your usage by the day. However the graph doesn’t make intuitive sense to me. Some days the indicated usage will randomly double. Other days I am sure I used a lot more electricity (window unit A/C on, for instance) but the graph is far lower than I expected. Does anyone have any insight into the accuracy of the indicated daily usage? Or maybe I am misinterpreting the results somehow (i.e. cutoff time for the day isn’t in fact 11:59 PM, etc.)?