A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Noell Wilson
Date: 2017 Apr 19, 19:55 -0700
Please see: http://www.sliderules.info/collection/nonstandard/023-gunter.htm
The Gunter rule seemed to be in a state of change and was apparently copied by others. I'd guess that each step was claimed to be "improved". The claimed main improvement was that the Gunter scale could be used like a slide rule instead of having to use log tables.
I had a hard time reading the rule in your photos but the rule in the example above seems to be fairly comprehensive - except for the errors found in the scales. :-(
They apparently had the necessary nav functions of a modern slide rule plus an hour to degree conversion scale. Many seemed to be two feet long so accuracy possibly could have been somewhat better than a new-ish 10" slide rule.
I suspect that there were some errors made on a rolling, candlelit, ship.