It's sometimes hard to visualize just how complicated simple things like basic calculations could have been in the age before digital calculators.
After all, there were centuries upon centuries when people couldn't rely on a simple slab of plastic with buttons to solve all their mathematical questions.
If you think of a time before digital calculators, it might be tempting to imagine an abacus and chalkboard, but there's actually a middle ground.
For a few decades, mechanical calculators ruled the roost, with finely-tuned cogs and gears helping to solve mathematical equations, and a photo of one went viral on Reddit this week.
It shows a mechanical calculator from a side-on view, with the casing of the device removed to show at least some of its internal workings.
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It reveals a wildly complex and intricate piece of machinery, one with pretty much countless levers that all work in chorus to come up with answers.
The machine looks much like a typewriter but is significantly more complicated than that.
Part of what's amazing about this image is the fact you can only really see some of the complexity of the design - it's not a full cross-section, so there's a lot that's still hidden.
It's unsurprisingly caused all sorts of discussion on Reddit, where the original post has racked up more than 11,000 votes to hit the front page.
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The top comment under the piece takes a very practical approach, reading: "That looks like a nightmare to maintain."
They're spot on, too - if a digital calculator breaks (which rarely happens) it's probably a question of software, but this thing looks like it could have all manner of hardware faults to check off.
Another commenter wrote: "This must have been a huge expense back in the day, that is a complex system."
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They're pretty much on the money - when these devices were first starting to spread onto the open market, in the mid-1800s, they were fairly exclusive since they were largely the preserve of mathematicians with a need for them.
Unsurprisingly, though, the mechanical calculator industry took a pretty steep nosedive toward the end of the second half of the 20th century.
After all, this was the exact time period in which digital computing was exploding, which would quickly make these cumbersome and complex devices entirely obsolete.
However, returning to that photo on Reddit, one hugely popular comment proved that you can always trust the internet to look at something a different way. One person wrote, to widespread agreement: "Looks like an Air Jordan designed by the Terminator."