About 15 years ago, our Bank purchased a banknote processing machine that could count and authenticate hundreds of banknotes per minute, separate the clean notes from mutilated ones and package or destroy them accordingly. Previously, the process was done manually, with our Currency staff hand-counting the banknotes, but this machine automated the process and produced reports that our internal audit team vetted and approved.
Having that machine should have drastically improved both efficiency and productivity, but initially, it did not. Why? Because one member of staff was not comfortable signing the reports until she had verified, by hand-counting, that the stacks of clean notes were the same number the machine had recorded. That was clearly an example of parallel testing!