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If you need more precision it is possible to enter exact values under "Lower base" and "Upper base"; the values under "Spikes" are for information only (they can be changed, but the values will not be considered).
The "Crown Shape" tab is subdivided into three sections:
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Here you find the coordinates of the spikes' control points. These values are for information only (: they can be changed, but the values will not be considered).