When designing a Custom Set Quilt, on the LAYOUT tab there is the option to Maintain the existing block sizes while resizing the layout.
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For example, here is a quilt with the center measuring 24 x 24.

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If the size of the quilt is changed to 48 x 48 with Maintain the existing block sizes while resizing the layout unchecked it looks the same because the blocks are resized along with the quilt.

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If the size of the quilt is changed from 24 x4 24 to 48 x 48 with Maintain the existing block sizes while resizing the layout checked there will be extra space to work with.
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If the size of the quilt is changed from 48 x 48 to 36 x 36 with Maintain the existing block sizes while resizing the layout checked the quilt center will surpass the borders.
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