If the duration or resolution of data is such that the number of points exceed the maximum number of horizontal pixels available on the screen, then the charts component does some aggregation of its own, to aggregate the points to fit the number of available pixels.

This aggregation is done additionally to the Graph Type and Resolution settings, and the available number of pixels will vary depending upon screen resolution.

If the maximum has been exceeded, and the charts component is doing its own aggregation, then the Charts Approximation options appear:

The default is to Average the data, but there are also options for Max and Min.

It is important to understand that this approximation is done in addition to the Graph Type and Resolution settings. So data is effectively being aggregated twice.