88 Geometric Dimensioning and Tolerancing Datum Features Specified Individually When multiple datum reference frames exist and features need to be positioned to different datums individually, then a note can be placed next to the datum feature symbols identifying how many datum features are to be considered separately. For example, if there are two separate datum features that are identified with the same datum identification letter, but they need to be considered individually, the note 2X INDIVIDUALLY is placed next to the datum feature symbols. An example of this can be seen on the SAW GUIDE FIXATION BLOCK drawing in the Prints for Print Reading Exercises section. This drawing has four holes at different angles. The holes on the right side need to be positioned to different datums than the holes on the left side. Instead of calling out two more datums and having to cut another section to show the holes on the left side, the datums are used individually and the locations of two holes on each side are positioned to the two datums individually. Using this method, only two holes are checked for position at a time to different datums. Datum Target Symbols In many situations it is not possible to establish an entire surface, or entire surfaces, as datums. When this happens, datum targets can be used to establish datum planes. Datum targets are designated points, lines, or surface areas that are used to establish the datum reference frame. This procedure is especially useful on parts with surface or contour irregularities, such as some sheet metal, sand cast, or forged parts that are subject to bowing or warpage. However, datum targets can be used on most parts. Use datum targets to minimize the variation in the way features are measured. This method can also be applied to weldments where heat can cause warpage. Movable datum targets are datum targets that are not fixed at their basic location, are free to translate, and can apply to a point, line, or area. The datum target symbol is drawn as a circle using thin lines. The circle is divided into two parts with a horizontal line. The bottom half provides the datum reference letter and the specific datum target number on that datum. The top half is left blank if a datum target point or line is identified. When identifying a datum target area, the top half contains the shape and size of the area. The dimension for the datum target area can be placed outside the datum target symbol with a leader and a dot pointing to the upper half if the dimension is too big to fit inside. See Example 3-13. When the datum target area is circular, a diameter symbol precedes the size value. When the datum target area is square, a square symbol precedes the size value. The datum target area can also be rectangular in shape, which is dimensioned with a length and width value, such as 10 X 25. The rectangular dimension is placed outside the datum target symbol and a leader points to the top half of the datum target symbol. A spherical datum target area can be used by placing the spherical diameter symbol in front of the size value. The spherical diameter is generally placed outside the datum target symbol and a leader points to the top half of the datum target symbol. The surface upon which the datum target lies can be identified with a datum feature symbol, as shown in Examples 3-14 and 3-15. A movable datum target symbol is used to indicate that the datum target is not fixed at its basic location and is free to translate. Refer to Example 3-13.