Create:
PROC [
parent: ViewerClasses.Viewer, -- the containing viewer
x, y: INTEGER ← 0, -- location within the parent viewer
diameter: INTEGER ← 16, -- diameter of the pie chart
total: REAL ← 100, -- number of units in the whole pie
divisions: NAT ← 25 -- the granularity of the display
] RETURNS [pieViewer: PieViewer];