A beautiful example of a late 18th Century or perhaps early 19th Century one foot Plain Scale used for navigation. 

These are usually not named as to maker - and this one is no exception. Diagonal scales on one surface, with several scales found on the Gunter rules on the other - Rum, Cho, Sin, Tan, S:T, Lea, M:Lon etc. Tiny brass gauge points for use with a compass. No splits or significant chips. All scales legible.