'SLIDING SCALE FOR CORRECTING LONGITUDE AT NOON, FOR AN ERROR IN THE LATITUDE USED IN THE COMPUTATION AT TIME OF SIGHTS, BY GILBERT, T. KEY, LIEUT. R.N.' J.D. POTTER, LONDON, C.1865
signed on the top plate J.D. Potter / 31, Poultry, London and comprising three card discs inscribed True 45º Bearing; Latitude 0º and Error in Latitude conjoined by a central brass stud, instructions and examples printed on the top plate, the reverse with manuscript inscription reading Rec Feb 7th 1865 at [?] Fort Menrue. -- 6¼in. (16cm.) diameter

John Dennett Potter worked between 1851 and 1880 from this address with a second establishment running from King St. from 1884.

Condition Report
Time-stained overall, structurally in good order, paper remains strong and readable.

We are pleased to provide you with a general report of the condition of this property. Since we are not professional conservators or restorers, we urge you to consult with a restorer or conservator of your choice who will be better able to provide a detailed, professional report. Prospective buyers should inspect each lot to satisfy themselves as to condition and must understand that any statement made by Charles Miller Ltd is merely a subjective, qualified opinion. Prospective buyers should also refer to any Important Notices regarding this sale, which are printed in the Sale Catalogue. NOTWITHSTANDING THIS REPORT OR ANY DISCUSSIONS CONCERNING A LOT, ALL LOTS ARE OFFERED AND SOLD “AS IS” IN ACCORDANCE WITH THE CONDITIONS OF BUSINESS PRINTED IN THE SALE CATALOGUE.