&quot;Many years later we asked our customers whether they wished us to provide an option to switch off these checks in the interests of efficiency on production runs. Unanimously, they urged us not to - they already knew how frequently subscript errors occur on production runs where failure to detect them could be disastrous. &quot;<p>I&#x27;ve always liked that part. Once they saw the problems, they&#x27;d put up with whatever sacrifices it took to avoid them.