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26 The PCB Design Magazine • March 2014 Wouldn't life be great if everything fit to- gether perfectly? There would be no need for tolerance. However, for that to be the case, ev- erything would need to be ideal and without variation. Therefore, unfortunately (or, maybe, fortunately), we all deal with measurements and materials and situations that are not ideal and are compromised in one way or another. Often the challenge with tolerance comes down to misunderstanding, and the fact that we all now design with CAD tools which have levels of precision far in excess of the realisable parameters of the mechanical or electrical ma- terials and measurement systems we deal with on a day-to-day basis. Poor understanding of tolerance or being intolerant of tolerance can lead to disappointment (see Figure 1). Or, as attributed to Aristotle, "It is the mark of an educated mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness where only an approximation is possible." That trans- lation itself is, of course, only an approximation and requires an appropriate degree of tolerance, but you get the idea. Looking back a few decades, it is clear that the challenge in terms of tolerance and dimen- sioning shifted with the move from analog to digital measurements, and electrically there is the beginning of a second shift where high- speed digital systems blur back into the analog realm. feature by Martyn Gaudion PolAr insTruMenTs Tolerant of Tolerance?

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