The part of a line that connects two points. It has definite end points. Adding word “segment” is important, because a line normally extends in both directions without end. The figure shows a line segment AB with point C. Point C can divide line segment in any ratio.

The scale on larger, fixed portion of calliper. It gives most significant digits in reading, while vernier is sliding portion giving least significant digits in reading. It can be furr divided into sub-parts as internal jaws, external jaws, locking screw etc.

Trochoid is a curve generated by a point fixed to a circle, within or outside its circumference, as circle rolls along a straight line and if points would had have been outside circumference of circle n it would have been called as superior trochoid. The below diagram shows a superior trochoid.

The bisector of an angle is a ray whose end point is vertex of angle and which divides angle into two equal angles. For figrure given below BD line is angular bisector dividing angle ABC in two equal parts.

Centre line is used to indicate axes of cylindrical, conical or spherical objects. Also to show centre of circle and arcs. Long, thin chain line composed of alternate long and dot spaces approximately 1mm apart. Long dashes are about 9 to 12mm apart.

Two or more circles with same centre and different radii, are termed as concentric circle. Inscribed circle is largest possible circle drawn inside a polygon, each side of polygon must be tangent to circle, while a circle containing a polygon in its interior touching all vertices of a plane figure is called circumscribed circle.

Let (x, y) be co-ordinates of any point on locus traced out by moving point P. Then we shall have
x = a cos ? or x/a = cos ? and y = b sin ? or, y/b = sin ?
x²/a² + y²/b² = cos² ? + sin² ? or, x²/a² + y²/b² = 1
which is required equation to locus of P.

The circle with diameter AB, excluding points A and B will be locus of point AB. This point P will always make 90� angle with circumference when lines from two points of radius meet at P, also from circle postulate it is proved.

In lettering ?A? type, height of capital letter is divided into 14 parts while in lettering ?B? type it is divided into 10 parts. The height of letters and numerals for engineering drawing can be selected from 2.5, 3.5, 5, 7, 10, 14 and 20 mm according to drawing size.

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