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The anchor icon indicates which custom frame item is the anchor frame.
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An anchor frame is a reference frame for a task used to align the workpiece with the path mounting frame of the device.
Any frame can be set as the anchor frame by hovering over the frame and selecting the Set as anchor frame button.
When a frame is marked as the anchor frame, the frame cannot be edited in the viewport.
Frames that are not marked as the anchor frame can be edited in the viewport.
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The Visible/Hidden button allows you to hide or show the frame in the task viewport.
Frame editor
When a frame is selected in the Custom frames panel, the Frame editor on the right shows values for it.