In the hole-to-hole system, all dimensions in the same plane are measured for the lines that define the critical holes. The baseline is not, in this case, a physical line, but is the center line between the critical holes.
(8) Coordinate System. The coordinate system is a dimensioning system based on the mathematical x-y coordinate system. It is usually only used to dimension an object that contains a great many holes, for example, an electrical chassis. It is particularly well-suited to computer use and to numerically controlled tape machines.
Each hole on the given surface is located relative to an x-y coordinate system, then all values are listed in a chart. The overall dimensions are not included in the chart but are located on the picture part of the drawing. Figure 75 is an example of an object dimensioned by using the coordinate system.
(9) Tabular Dimensions. Often manufacturers will produce a part in several different sizes. Each part will have the same basic shape, but the part will vary in overall size. To save having to dimension each part individually, a system called tabular dimensioning is used. Figure 76 (on the following page) illustrates an example of tabular dimensioning.
To read tabular dimensions, look up the part number in the table and substitute the given numerical values for the appropriate letters in the figure. For example, part number 1003 (according to the table) has an A value of 2.25, a B value of 1.50, and so on. Part number 1005 has an A value of 2.50, a B value of 1.75, and so on. The numerical dimensions of .50, located on the picture part of the drawing, mean that these dimensions do not vary, that they remain the same for all parts.
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