When comparing Dashboard graphs to Classic graphs, both allow showing min/max/average in the legend, but the behavior differs.

For example, having an item with four values [5, 50, 50, 95] would show the correct min/max values in the Classic graph legend (5 for min and 95 for max), regardless of the zoom level (time period) used for the graph itself.

But for the Dashboard graphs, those values are tied not to the actual item values for this period, but rather to the values shown on the graph (including all aggregations/approximations). So, for example, the last 15m will give me this graph:

The last 12 hours would give me this:

And the last day would give me a single value for min/avg/max:

And the whole situation gets even weirder when using the Approximation "all". Then I get the following values on the zoomed-in graph:

Yet for the zoomed-out version, min and max values don't seem to match the visual representation:

Overall, it seems that there are differences in the behavior of Classic and the Dashboard graphs, between actual behavior and the documentation, and possibly some implementation-related bugs.