Examples of these very similar octants are in the photos in this article. The image at the top is essentially the same instrument as the one in the detail photos. However, they are from two different instrument makers - the upper is labelled "Crichton - London, Sold by J Berry Aberdeen" while the detail images are of an instrument from "Spencer, Browning & Co. London". The only obvious difference is the presence of horizon shades on the Crichton octant that are not on the other.