Originally Posted by DARCY1
They were made for aircraft, but became surplus and so quite cheap. Many found their way onto all sorts of small craft despite being marked in degrees. However you didn't need to look at the degrees when steering. You merely had to set the grid to the required course and keep your heading between the white lines. The one I encountered was just like the one in the picture, and may have been a P6. It was a reasonably priced practical instrument for an ex torpedo boat. It was in a box like the one shown. The box was painted grey and had some markings that had the look of military stores.