Figure Baseline System

Reference Baseline Datum Dimensioning

(6) Baseline System. The baseline system of dimensioning is illustrated in figure 73 (on the previous page) . All dimensions in the same plane are located from the same line which is called a baseline. It is sometimes called a reference line or datum line. This system is particularly useful because it eliminates tolerance buildup, it is easy for manufacturers and inspectors to follow, and it is easily adaptable to the requirements of numerical tape machines. Its chief disadvantage is that the amount of space used on the drawing paper is larger--usually at least twice the area of the surface being defined. Also, once it is setup, it is difficult to alter.

When you use the baseline system, be careful to include all needed dimensions and be sure to use a large enough piece of paper.

(7) Hole-to-Hole System. The hole-to-hole system is illustrated in figure 74. It is a modification of the baseline system used to dimension parts whose hole-to-hole distances are critical; for example, a part that must be aligned with the shafts or dowels of another part for proper assembly.

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