&gt; <i>Therac-25 UI was essentially a CAD program</i><p>Clever comment! But wait, is that really the Therac-25 you&#x27;re thinking of?  The Therac-25 was basically just a bug-trap of assembly language race conditions, that&#x27;s all.<p>There was another similar case of a radiation machine in which the dose was supposed to take into account the shield. The user could draw the shield with a CAD-like plannning program. The users tried to draw a shield with a cutout, and the CAD display led them to believe that the shapes were being subtracted. (The filled path was drawn with the in-out rule or whatever.) The actual dose calculation though ignored this and added the negative area as a positive. Whoa, you have lots of shielding, crank up the radiation! Or something like that.<p>This is not actually the radiation machine but the treatment &quot;planning&quot; software. (It meets the definition of CAD: it&#x27;s computer software, and it&#x27;s assisting in the design of something: the treatment.)<p>Gee what was this? Perhaps that circa 2000 incident in Panama?<p><a href="http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;17199912" rel="nofollow">http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;17199912</a><p>This is a very informative report with all the details, including diagrams:<p><a href="http:&#x2F;&#x2F;www-pub.iaea.org&#x2F;mtcd&#x2F;publications&#x2F;pdf&#x2F;pub1114_scr.pdf" rel="nofollow">http:&#x2F;&#x2F;www-pub.iaea.org&#x2F;mtcd&#x2F;publications&#x2F;pdf&#x2F;pub1114_scr.pd...</a><p>(See P. 22 for instance)