That doesn't mean that they're wrong. You can take a look at early 20th century literature to see the sorts of mental math humans (especially humans employed as "computers") were capable of.
Even further back, you can take a look at how good human memory was in oral-tradition, preliterate cultures. All of those extremely long poems had to be memorized by bards, skalds, griots, etc.
Even further back, you can take a look at how good human memory was in oral-tradition, preliterate cultures. All of those extremely long poems had to be memorized by bards, skalds, griots, etc.