As far as I'm concerned, the first true pocket calculator (as opposed to hand-held) was the HP-35. It was also a full scientific calculator.
The mistake the technician made was not swapping op-amps with a working filter. This would have confirmed whether the op-amp was defective.
No one would deny the hard work and genius of the designers. But aren't you forgetting something? Can you say "Hewlett Packard"?
I'm good at teaching myself how to do something. But I'm also easily distracted. There are so many other interesting things...
At least it was a challenging test.