Hybrid Assistant uses "bubbles" to represent data on scatter charts.
Size and color are proportional to accuracy of the data point represented.
Check the following chart, that depicts relationship between RPM of the petrol engine and kW produced.
For each RPM value, all kW measured at that regime are averaged and plotted.
A blue, large dot is made up from few collected values, so it's precision is low and the plotted point may be affected by statistical errors.
An orange, medium dot is plotted when more data is available and precision is higher.
A small red dot means that a sufficent samples were collected to have a reliable value.
Longer trips lead to more defined charts.