A gauge point is sometimes marked at 1146 on the A and B scales. This is known as the “Gunner’s Mark,” and is used in artillery calculations involving angles of less than 20°, when, for the purpose in view, the tangent and circular measure of the angle may be regarded as equal. For this constant, the angle is taken in minutes, the auxiliary base in feet, and the base in yards. The auxiliary base in feet on B is set to the angle in minutes on A when over 1146 on B is the base in yards on A. The value (1)/(1146) = (π × 3)/(180 × 60). TABLES AND DATA. MENSURATION FORMULAE. Area of a parallelogram = base × height. Area of rhombus = ½ product of the diagonals. Area of a triangle = ½ base × perpendicular height. Area of equilateral triangle = square of side × 0·433. Area of trapezium = ½ sum of two parallel sides × height. Area of any right-lined figure of four or more unequal sides is found by dividing it into triangles, finding area of each and adding together. Area of regular polygon = (1) length of one side × number of sides × radius of inscribed circle; or (2) the sum of the triangular areas into which the figures may be divided. Circumference of a circle = diameter × 3·1416. Circumference of circle circumscribing a square = side × 4·443. Circumference of circle = side of equal square × 3·545. Length of arc of circle = radius × degrees in arc × 0·01745. Area of a circle = square of diameter × 0·7854. Area of sector of a circle = length of arc × ½ radius. Area of segment of a circle = area of sector − area of triangle. Side of square of area equal to a circle = diameter × 0·8862. Diameter of circle equal in area to square = side of square × 1·1284. Side of square inscribed in circle = diameter of circle × 0·707. Diameter of circle circumscribing a square = side of square × 1·414. Area of square = area of inscribed circle × 1·2732. Area of circle circumscribing square = square of side × 1·5708. Area of square = area of circumscribing circle × 0·6366. Area of a parabola = base x ⅔ height. Area of an ellipse = major axis × minor axis × 0·7854. Surface of prism or cylinder = (area of two ends) + (length × perimeter). Volume of prism or cylinder = area of base × height. Surface of pyramid or cone = ½(slant height × perimeter of base) + area of base. Volume of pyramid or cone = (⅓)(area of base × perpendicular height). Surface of sphere = square of diameter × 3·1416. Volume of sphere = cube of diameter × 0·5236. Volume of hexagonal prism = square of side × 2·598 × height. Volume of paraboloid = ½ volume of circumscribing cylinder. Volume of ring (circular section) = mean diameter of ring × 2·47 × square of diameter of section. SPECIFIC GRAVITY AND WEIGHT OF MATERIALS.