To create a function using this command, use the Marker tool to draw a curve on your coordinate system. With the drawing selected, choose Define Function from Drawing.

The selected drawing defines the value of the function, and the width of the drawing defines its domain. If the drawing crosses itself or doubles back horizontally so that more than one part of the drawing corresponds to a given horizontal position, the highest part of the drawing determines the function value for that horizontal position.

Import a picture, either by dragging and dropping into your sketch or by copying from some other document and pasting into Sketchpad. With the picture selected, choose Define Function from Picture.

The top edge of the picture defines the value of the function, and the width of the picture defines its domain.