How it works...

The type attribute on a graph element determines the initial mode of a graph view. Possible values are bar, line, and chart, while bar is the default. The graph view is highly interactive, so the user can switch between the different modes and also add and remove fields. Pivot views have their own root element, pivot.

The field elements tell Odoo what to display on which axis. For all graph modes, you need at least one field with type row and one with type measure to see anything useful. Fields of type row determine the grouping, while type measure stands for the value(s) to be shown. Line graphs only support one field of each type, while charts and bars handle two group fields with one measure nicely. The pivot view supports an arbitrary amount of group and measure fields. No worries, things don't break if you switch to a mode that doesn't support the amount of groups and measures you defined. It's just that they'll ignore some of the fields and won't always show a very interesting result.