Yes, there was the massive Saturn V rocket and the LEM and the Command Module we’ve been hearing so much about in the run-up to Saturday’s moon landing 50th anniversary, but Neil Armstrong’s small step and giant leap began with millions of individual calculations on sliding pieces of wood with numbers on them: The slide rule.

It was the pocket calculator of its day, a way for mathematicians and engineers to make speedy calculations on a ruler-within-a-ruler, no batteries required.

For nearly a century, from 1891 until about 1975, millions of slide rules were cranked out of the Hoboken factories of Keuffel & Esser. One of their factories is now on the National Register of Historic Places, the Clock Tower Apartments on Adams Street in Hoboken.

The power of the slide rule lay in its ability to show relationships between numbers, on several different scales at the same time. It took the tedium out of calculations. A savvy engineer could multiply, divide, find the square and calculate complex logarithms simply by knowing which way to slide that middle piece of wood.

For Houston, no problem

To modern mathematicians raised in the age of the Watson supercomputer — which IBM says can process 500 gigabytes of information per second, the equivalent of 1 million books per second — the speed of the slide rule is staggeringly slow.

For example, here's how you would solve 2 x 4 on a slide rule.

Each slide rule has letters down the left side, at the end of each scale (or number line). In its closed state, all the numbers line up: the 1 over the 1, and so on.

To multiply, use scales C and D. Slide the C scale index (or end) to align with the number 2 on the D scale. Find the number 4 on the C scale. Look under the 4 to the D scale to find the answer: 8.

It's slow, but it's all NASA had at the time. And there's no arguing with the results.

You can see the slide rule — actually a lot of slide rules — in action in Ron Howard's 1995 film "Apollo 13," as Mission Control engineers feverishly figure out how to get a crippled spaceship back to earth.

They all perform the same calculation, one calculation, for confirmation.

Multiply that single calculation by the nearly 7 years it took to turn President John F. Kennedy's speech at Rice Stadium in Houston, Texas on Sept. 12, 1962 ("We choose to go to the moon") into footprints on the moon 82 months later and you have an idea of the scale of the achievement of getting Apollo 11 to the moon and back.

NASA engineers used the "slipsticks," as they were known, to build the rockets and plan the missions for the Mercury, Gemini and Apollo missions.

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Slide rules to the moon

Pickett slide rules flew on five of Apollo missions, a fact that the company crowed about in ads at the time.

In September 2007, Heritage Auction sold the Pickett slide rule that Apollo 11 astronaut Edwin "Buzz" Aldrin took to the moon.

The Pickett Model N600-ES (Eye Saver) Log Log Speed Rule, was 6 inches long with 22 five-inch scales. In 1969, the N600-ES sold for $10.95.

Aldrin's moon-used slide rule fetched $77,675 at auction.

More:Buzz Aldrin took communion on the moon. NASA had him keep it quiet

Days numbered

But the slide rule's days were numbered soon after those first footprints were placed on the lunar surface.

Barry de Versterre saw its demise, firsthand. Now a network engineer in the banking industry, he studied electrical engineering at Newark College of Engineering, which is now under the umbrella of the New Jersey Institute of Technology.

When de Versterre started at NCE in 1973, he looked the part of an engineering student.

"I wore a pocket protector, because Bic pens would drain right out," he said. "And, because you never knew when there was gonna be a hot math problem, I wore my slide rule on my belt.

"My first two years, freshman and sophomore, was 100-perent slide rule," he said. "During junior year is when calculators started coming in and some professors would allow calculators for their tests and others would not. By my senior year, the slide rule was gone. It was that fast."

De Versterre's father, William, was an engineer who used a bamboo slide rule he kept in a leather case. The elder deVersterre later helped develop test equipment for NASA's space shuttle program.

His son is still amazed at the achievement accomplished 50 years ago this week, when he was a Boy Scout at Camp Watchung in Glen Gardner, New Jersey, watching Armstrong's giant leap on a small TV set up in the camp's mess hall.

"Every calculation was done 18 times," he said. "You don't do that without many people running through the same calculations over and over again. And remember that we had to keep track of zeroes in our head. That was always something. When you multiply 10 times 20, that's two zeroes, so you've got to remember to keep track of it."

History, in Hoboken

While the invention of the original slide rule is credited to William Oughtred in 1622, Frenchman Victor Mayer Amédée Mannheim is the father of the modern slide rule, which he standardized in 1850 and used to calculate artillery and ballistics trajectories.

Amédée Mannheim’s contribution was to add the center sliding ruler. He was rewarded by having the device bear his name for generations. It was simply called “The Mannheim.”

When the slide rule came to America in a big way, it was largely due to two Germans who set up shop in Hoboken.

Wilhelm Johann Diedrich Keuffel and Herman Esser founded Keuffel & Esser in Manhattan and began selling slide rules — in addition to drafting tools and surveying instruments — in 1886.

In 1891, they began making their own slide rules at Third and Grand Street in Hoboken. The company survived its founders’ deaths to become the largest American maker of slide rules.

The 1960’s were heady times for K&E, fueled by the postwar building and engineering booms and The Space Race. All those engineers needed slide rules.

In 1967, K&E commissioned a study to cast its eye 100 years in the future. In 2067, the study concluded, we would be living in domed cities and watching 3-D TV’s. But what the report failed to predict was that within nine years, the slide rule would be done in by pocket calculators.

In 1976, Keuffel & Esser shut down its slide-rule factory and moved into computer-aided design. It was acquired by AZON in 1987.

Now, the slide rule is a novelty.

Last weekend, de Versterre went to a music festival and, perhaps fueled by moon-landing nostalgia, brought his slide rule along.

"People were asking questions," he said.

While there's nostalgia, he's not ready to go back to those days.

"I remember back in the day the TV had five channels and I stood up and I changed the channel," he said. "I'd be hard pressed to figure out how to turn my TV on right now without the remote. You spend an hour looking for it so we can change the volume. I do see the pluses and minuses, but then again I'm very happy for indoor plumbing."

Email: pkramer@lohud.com