Computalog Ltd. v.
copyright 1997 Donald M. Cameron, Aird & Berlis
Computalog patented a method for determining whether a plug of concrete was pure enough to seal off sections of an abandoned or completed well. A machine which measured the density of its surroundings was lowered down the well and passed through the wet concrete. Differences in density from the ideal density of the drilling mud, or the slurry indicated contamination.
Comtech claimed it used the claimed technique, but not to measure contamination but rather to locate the concrete.
At p. 301
As to substantial infringement, it is abundantly clear, as mentioned earlier, that the essence of the patent in issue is a method to determine the quality or purity of the cement slurry in a plug, whereas the method used by the defendant is not to determine the purity of the cement slurry but to establish the location of the plug in the borehole. The two objects are not the same and the methods used to achieve them are different.
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