A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bill Morris
Date: 2017 Feb 5, 19:14 -0800
At least one other aeronautical sextant was held in the left hand: Brandis Model 206 C of 1931. I give details here: https://sextantbook.com/category/unusual-left-handed-sextant/ By 1935 Plath was making right handed Coutinho sextants.
I can think of one avantage to the left handed instrument: it allows a right handed person to write down results without setting down the sextant. If the navigator was also the pilot this may have been seen as an important detail. Brandis also placed the legs on the face of the instrument so that if it was set down, there was no need to juggle hands, but Plath did not have this detail.
Commander Bauer makes the same points on page 45 of his "The Sextant Handbook".