The Analog Device That Put Humans on the Moon
February 4, 2025
Source: Polyplastics
Before smartphones, before pocket calculators, before computers were everywhere, there was the slide rule. It may look like just an old ruler with too many numbers, but this simple tool played a huge role in some of the biggest achievements in human history—including landing on the Moon.
What Is a Slide Rule?
If you’ve never used one, a slide rule might look confusing at first glance. But for over 300 years, it was the go-to tool for scientists, engineers, and mathematicians. This mechanical calculator uses logarithmic scales to help users quickly multiply, divide, and solve more complex math problems like exponents and trigonometry.
Unlike a regular ruler, the sliding middle section allows numbers to line up in ways that make math faster—no batteries required. Before digital calculators, this was the ultimate math tool.
How the Slide Rule Helped Land Astronauts on the Moon
The Apollo missions were some of the most daring projects ever attempted. Computers back then were slow, massive, and had way less power than even a basic modern smartwatch. NASA engineers needed a quick, reliable way to do calculations, and the slide rule was the answer.
Rocket trajectories, fuel loads, landing speeds—these critical calculations weren’t done on a fancy screen but by engineers using slide rules. Even astronauts carried them as a backup in case onboard computers failed.
One model, the Pickett N600-ES, even made the trip to the Moon with Apollo 11. Buzz Aldrin himself had one in his personal kit. In an age of paper checklists and manual controls, this was the kind of tool that could save lives.
The Rise and Fall of the Slide Rule
For decades, every engineer and scientist had a slide rule in their pocket or on their desk. Universities taught students how to use them, and businesses depended on them for complex calculations. But in the 1970s, everything changed.
The electronic calculator arrived, and within a few short years, slide rules became obsolete. By the 1980s, they had all but disappeared. What once was an essential tool was suddenly a relic of the past.
Why It Still Matters Today
Even though no one really uses them anymore, slide rules still have a certain charm. They remind us of a time when problem-solving required more than just typing numbers into a screen. Using one took skill, understanding, and a bit of intuition—something modern calculators don’t require.
Some enthusiasts still collect them, and a few schools even use them to teach math concepts. After all, knowing how numbers relate to each other is just as important as getting the right answer.
A Small Tool That Made Big Things Happen
It’s easy to dismiss an old slide rule as a forgotten piece of history, but it’s so much more than that. This simple device helped engineers design bridges, build airplanes, develop nuclear energy, and, most impressively, send humans to the Moon.
So if you ever find an old slide rule tucked away in a drawer, take a moment to appreciate what it represents—a time when brilliant minds, armed with just a simple tool, changed the world.