True Scale or Natural Scale is used to draw Orthographic Views. In these views, the viewer’s direction is exactly perpendicular to the plane of view,hence true Dimensions are seen. But in Isometric view, object is seen from an angle to get view of all three plane. A corner of the 3D object is the nearest point to the viewer and all other dimensions of the object are moving away from the viewer. So the dimensions APPEAR to be smaller than the true ones. This difference can be computed by the figure 10. Unit 1 on the natural scale appears to be Unit 1 on the Isometric scale.
Step in drawing isometric scale –
Ref.fig.11.10 draw a line at 45° and at 30°. Mark points on true scale and draw line perpendicular to X – axis as shown in the fig. Distance of point O from point on isometric scale is the length of object on isometric scale.