A compact mechanical computer by which the navigator can fix his position from a set of star sights in a few minutes. This is accomplished by means of:- (a) an internal degree calculator, and (b) the setting of an angled slide rule which converts time and arc increments into the correct E-W movement and automatically places a draughting instrument into the exact position from which to lay off the intercept.
On the left of the instrument is a multiple linear slide-rule mounted on a turntable. This is rotated and clamped so that the slide-rule is set at an angle equal to the assumed Latitude. On the right is a white perspex plotting board containing a short narrow E-W slit through which a pin projects upwards carrying a perspex protractor and graduated T-square.
In the lid of the case is a pivoted disc, graduated in degrees on which additions of integral degrees are done visually.
All sliding movement of the angled slide-rule is transmitted via a slotted bar and slider to the pin, the E-W motion of which will be in the ratio of the Cosine of the Latitude.