1. AutoCAD Release 12, Advanced Tools Manual, Autodesk Inc., 1993, Chapter 6.
2. Kunz, J. C., Jin, Y., Levitt, R. E., Lin, S. and Teicholz, P., The intelligent real-time maintenance management (IRTMM) system: support for integrated value-based maintenance planning. Technical Report 100, Center for Integrated Facilities Engineering, Stanford University, 1995.