Rounded eyelet (pattern)

This looks like a fairly complex pattern made up of larger, filled octagons joined together by smaller straight squares. In actual fact the pattern is easy to follow by completing a number of offset eyelets and then outlining each eyelet with a octagonal frame.
Method
1
Start by completing a single diagonal stitch across one thread and down over three threads.
2
Add another seven diagonal stitches of the same length all going down into the same hole to complete an eyelet.
3
The next eyelet should be offset from the last, but touch at the corners.
4
Fill the area with a pattern of offset touching eyelets.
5
Each eyelet should then be framed with an octagonal outline.
6
Continue to outline the eyelet pattern with the octagons.

Embroidery Techniques
References
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Various Authors, The Royal School of Needlework Book of Embroidery (2018) , p.151