This device consists of a boxwood board 7.5 x 5" (19 x 12.7cm), at two sides of which are metal rollers for securing a roll of paper and for keeping it stretched across the board. The rollers are rotated by means of knurled brass knobs.
A rotating compass is set into the head of the board and has an outside scale graduated every 10degs. There is also an indicator line for showing the "working meridan". A leather wrist strap is attached to the back of the board. This example is fitted with a Royal Cruising Club chart instead of a paper roll. The chart would appear to date from about 1929.