Hidden Lines, Center Lines and Dimensions
In isometric drawings, hidden lines are omitted unless they are absolutely necessary to completely describe the object. Most isometric drawings will not have hidden lines. To avoid using hidden lines, choose the most descriptive viewpoint. However, if an isometric viewpoint cannot be found which clearly depicts all the major features, hidden lines may be used. eg. Figure 8(a). Centerlines are drawn only for showing symmetry or for dimensioning. Normally, centerlines are not shown, because many isometric drawings are used to communicate to non-technical people and not for engineering purposes.

Figure 8 showing hidden lines and centre lines.

Dimension lines, extension lines, and lines being dimensioned shall lie in the same plane. All dimensions and notes should be unidirectional, reading from the bottom of the drawing upward and should be located outside the view whenever possible.  The texts are read from the bottom, using horizontal guidelines as shown in Figure 9.

Figure 9 showing the procedure of using dimension lines, extension lines and text.