A silk text is a particular kind of silkscreen that lets you add text to your PCB.
A silk line is a line that stretches between two specified points. You can use a line path rule for any desired curves.
A silk circle is a circle with a specified origin and diameter.
A silk rectangle stretches between two specified points.
The stroke length, spacing, style, width, and width of these three silk elements can all be modified using the appropriate rules."
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Want me to walk you through setting the two points so the rectangle is exactly 33 mm by 20 mm?