@Bjorkdidit
And yet if you tell them that in my day, we used to add everything up in our heads/on paper and work the change out without any help from an electronic till and they won't believe you
Yes, it's true. My parents bought a corner newsagents in 1974. We didn't have an electric till. Everything was added in our heads, along with working change (which was actually very easy when you use the "count up" method). Not only that, but we had two till drawers, one for zero VAT rated items such as newspapers and another for standard rated items such as chocolates, sweets, greetings cards, cigarettes, soft drinks, etc. So we'd have to add everything up twice, one for a total for the customer to pay, and then we'd have to do a separate tally to transfer the different VAT rated monies from one till to another, where, say the customer had bought a newspaper and packet of Benson & Hedges.
I was only ten, but inevitably I rapidly gained brilliant mental arithmetic skills as I used to serve the counter with my parents.
It was about 20 years later that we bought an electric till, and God, it was slow. Pressing the buttons etc was a hell of a lot slower than just adding up in our heads, but at least we didn't have to fart around with two different till drawers anymore.
I still do the adding up in my head when I go shopping and keep a mental tally of a running total of how much I'm spending. If the till shows a different figure, I'll challenge it, and it's usually something that's been shelf marked wrong or a BOGOF or other offer that hasn't been applied correctly in the till. But usually, it's spot on to the exact amount I added.
Calculators, phones, tills, etc really do make our minds lazy.