National Instruments Graphical User Interface Ultiboard - Manual (Page 102)

Chapter 4 Working with Parts
NI Ultiboard User Manual 4-6 ni.com
Working with Force Vectors
Force vectors are powerful aids that help you place parts on the PCB. When
you place a part manually on the board, you should pay careful attention to
the force vectors coming from that part. They allow you to place the part as
close as possible to other parts that are attached to the same net.
Try to minimize the ratsnest distances from that part to other pads on the
board. Force vectors work by treating the force vector lines coming from
each part as if they were vectors, adding them together as a vector sum, and
producing a resultant force vector. The resultant force vector has a length
and direction. By moving the part in the direction of the force vector, and
trying to minimize the force vector length, you are moving the part to a
location that results in the shortest possible combination of ratsnest lines.
Note Force vectors are extremely valuable as a guide, but you should not follow them
blindly. By the nature of the algorithm, all force vectors have a natural tendency to point
toward the center of the board, because all ratsnests would have their shortest connections
if all parts were located directly on top of each other in the very center of the board.
In Ultiboard, force vectors are represented by colored lines, although they
can be dimmed. They appear by default, but can be controlled through the
Information section of the Layers tab in the Design Toolbox. Refer to the
Accessing Layers section of Chapter 3, Setting Up a Design , for more
information about dimming and hiding force vectors.
The figure below shows force vectors coming from parts.