The measure geometry window show angles, distances and areas for the currently active measure (which is displayed in the Digitize toolbar).
At each point, the angle is defined between the line from the previous point, and the line to the next point.
At each point, the distance is defined as the length of the line to the next point.
The functional area of the measure is the area calculated by integrating the area under the curve. The polygonal area of the measure is the area within the polygon through all of the points in the measure.
Until the coordinates are defined by axes points or a scale bar, the measure geometry window will show information in the screen coordinates, which are in units of pixels. Afterwards, the geometry measurements are in the measure coordinates.