Arbortext IsoDraw > User's Reference > Palette Window Toolbox > Ellipse Value > Standard Ellipse
  
Standard Ellipse
Three major axes are defined in each parallel perspective. The X axis and Z axis are represented by the active grid. The Y axis is always vertical and therefore never appears in the representation.
Each major axis features exactly one ellipse which represents a circle on this major axis. The three ellipses on the three axes do not necessarily have to be the same, they are only identical in isometric perspective.
If you select the Standard ellipse option, ellipses, threads or polygons are generated during dragging which lie on one of the major axes.
If you need to draw ellipses lying outside the major axes, you generally cannot use the Standard ellipse ellipse value. Instead use Element > Find Ellipse to generate the appropriate ellipse.
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In most cases, you won't need to know the actual value of the ellipse value. If, however, you do need to know this value, you can always look it up at any time in the element info dialog box.