Rectifier

in navigation, an instrument consisting of two parts, which are two circles either laid one upon, or let into, the other, and so fastened together in their centres, that they represent two compa es, one fixed, the other moveable; each of them divided into the thirty two points of the compa , and three hundred and sixty degrees, and numbered both ways, from the north and the south, ending at the east and west, in ninety degrees.