Circular slide rule provides for solution of time, speed and distance, fuel consumption, conversions, multiplication and division.Face of Vectormaster permits rapid solution of problems involving vectors, such as those encountered in current sailing, determination of true wind direction and force and apparent wind to be expected on other headings.Given position of a storm and direction and speed of its advance, you may quickly determine course which will put maximum distance between your vessel and oncoming storm.Instruction booklet included.Dims: 7" (178 mm).Weight 0.25 lbs. (114 g).