One is the statistics button in the legend editor, the other is the histogram function on the button bar. . Both do the obvious. Go into the legend editor by double clicking on the theme. Since you re in the Legend Editor, play around with different color schemes for the elevation data. The Quadrangle is in the UTM coordinate system.
Map units are therefore meters.
However, elevation units are in feet. Otherwise you get slope garbage. Lets convert this DEM from feet to meters. To do this, we generate a new grid that is in meters. There are 3.2808 feet per meter.