Last spring, I took the AP Calculus Examination. Taking the test was not my idea; everyone in an AP class in my high school was required to take the May exam. I am not, suffice it to say, a math person, so I studied months before the actual test hoping to master the material. (Spoiler alert: I did not master the material.) It was a miserable, tough slog—until my world was turned upside down by a practice free response question.

The calculus problem in question was from the exam published in 1991. My teacher had given us enormous packets with practice tests from a variety of years, and my classmates and I worked our way through them painstakingly: 10 AP tests x 15 pages per test x 10 years = a lot of problems. When I glanced at the top of the page and saw that the date of the test was 1991, though, I was flabbergasted. I might have even let out a small gasp, something that was probably interpreted by my tablemates as my routine reaction to seeing a logarithm.

The question might have involved a logarithm, but that wasn’t the most alarming part. I was flabbergasted because I was doing the same problem as high school seniors who would not for another 18 months know that Bill Clinton would be sworn in as the 42nd president of the United States.

I was flabbergasted because I was doing the same problem as students who lived in a world without Russia or Taylor Swift or YouTube, a world with apartheid in South Africa and 85 cents for a dozen eggs in America.

I was flabbergasted because I was writing the same numbers as high school seniors who would not for another 10 years turn on the news to see that two planes had crashed into the World Trade Center, one into the Pentagon, and one into a field in rural Pennsylvania.

I was flabbergasted because I was reading the same question as high school seniors who would not for another 20 years witness a demonstrative campout in downtown Manhattan that would spread across the country, sparking literally hundreds of protests known collectively as Occupy Wall Street.

The teenagers who were doing my math problem, which I had claimed my own after ruminating on it for 10 minutes while all of my friends had moved on, in 1991 were probably wearing MC Hammer pants, hoop earrings, and shoulder pads. They were probably sporting headphones plugged into a Walkman blasting “Good Vibrations,” Marky Mark and The Funky Bunch’s hit. But they were also drawing their integral signs just as I was drawing mine; they were crossing their t’s just as I was crossing mine; they were furrowing their brows in confusion just as I was furrowing mine.

Few things are as timeless as math. Even history changes from year to year, if not the facts then the way they are phrased. What was politically correct in a science or English classroom in 1991 is probably not politically correct today. Say what you will about math, but at least X will always be X.

I’ve always been fascinated with time capsules; that sort of thing really gets me going. I’ve buried at least one object in the backyard of every home I’ve ever occupied, to symbolize my tenure there, but I usually forget about these objects until after I’ve moved—and way beyond the point of it being socially acceptable to retrieve them.

I imagine myself timorously making my way up the front steps of 3 Robert Chrisfield Place or 190 Stuyvesant Avenue, and asking to locate my capsule. I imagine the people who live there now (or, in the case of 190 Stuyvesant, the family of raccoons) cautiously nodding. I imagine myself leaving in defeat, empty-handed and apologizing for the small craters left in my wake. I doubt that I’d be able to find any of the things I’d buried; I not only don’t remember where I buried them, I also don’t remember what I buried.

Objects clue us into the things we valued, the thoughts we had, the numbering of our priorities. The tattered owl for which I had so much affection as an eight-year-old means nothing to me now; the plastic whistle I loved at age five is now a useless piece of plastic. That’s why, I think, I was so blown away by the teenagers doing my math problem in 1991. I didn’t expect the math to change, but I did expect it to mean something different, and the fact that it meant the same thing in 1991, or 1995, or 2004, is jarring.

Time is weird. Math makes it weirder. Whole lives are built around the same formulae and practice problems. Numbers don’t have to be sterile, but sometimes they are. Maybe sometimes we need an anchor, a constant—pun intended—that links us to our 90s counterparts. Math is the same in all languages, a fact that brought Lindsay Lohan’s character in “Mean Girls” unending glee, and understandably so: it’s refreshing to have such easy, direct links.

Math isn’t a clue to the past. It’s a reminder of the present.

Davis is a member of the class of 2017.