The soul-full song of a harmonica drifts through the halls of the dungeons, echoing through empty cells and dusty spaces. Someone would have to do something pretty sinister to deserve incarceration here. Since ponies are a naturally friendly and innocent sort, the dungeons beneath Canterlot Castle had gone mostly unused for the last hundred years or so.

Now they had a new resident, a bubbly pink pony that looked very out-of-place among the dark stone and cold steel bars. Despite the conditions around her, her mane remained poofy and her fur bright. The harmonica against her lips was singing like the walls around them might crumple from the sound.

Pinkie Pie was exactly the kind of pony to deserve imprisonment here. Her crimes were nearly unfathomable. She had committed a truly heinous atrocity.

She made an old lady cry. Twice.

It all started about a week ago, directly following the unprecedented success of Operation P.A.N.C.A.K.E..

Pinkie pie

Arbitrarily

eats some paN-

Cakes

And

Kleans up the

mEss afterwards

Her next mission, use the word archaeomagnetism in a sentence. Her first stop in this endeavor, her sister Maud's house.

Fresh off her rocktorate and living in a gem cave, Maud was a relative expert in the field of all things rock and mineral. If it was hard and underground, she probably knew about it. A lot of stuff underground was super duper old, too! So if anyone might know about dating things using archaeomagnetism, it was her.

On top of that, Pinkie hadn't visited in a bit and wanted to check in.

Luckily for Pinkie, Maud's afternoon was free and she was more than happy, almost ecstatic, to talk about her professional interests with her sister. That most of it went over Pinkie's head was only a minor setback. She borrowed one of Maud's old textbooks with the relevant information. On the way home, she also checked out a book from Twilight's personal library at her castle.

Two evenings of uninterrupted study in the party cave yielded the results she was looking for, but it wasn't enough. This project was too big for her. It was time to recruit the Princess of Peer Review herself.

"Heyyy Twi twi! Do you have a minute to talk shop with me? I've got a project and I need your help with it."

Twilight looked up from her work, glancing across the small mess of papers and folders that currently adorned the cutie map to where her friend had appeared. Twilight had noticed her coming through the door, which was strange enough considering Pinkie's penchant for popping up in random spots to pester her. That alone was enough to grab part of the purple pony's attention.

"I've got a moment, but I'm not sure how much help I can be. I'm no baker, and the last time I tried to experiment with a dish I ended up almost ruining your Hearth's Warming present. But as long as it's not pudding, I can do my best to assist."

Pinkie sat in her designated throne/chair and started to make an airplane from a blank piece of paper.

"No worries, friendo. This isn't kitchen related. It's about old things and dating them. But not the romance for elderly ponies kind-of-dating." The plane was certainly odd looking, and didn't seem very aerodynamic.

Twilight cocked her head to the side. "Wait, is this about your dictionary thing?"

"Exactamundo!" She tossed the plane, and it flew pretty good actually. "The word I'm currently working on is a tough one, and it requires some sciency-researchy stuff that I'm not really used to doing."

"What's the word?"

"Archaeomagnetism."

Twilight thought for a moment, considering the request. She now had a unique opportunity to both take part in one of Pinkie's schemes, while simultaneously getting to do something she personally enjoyed with a friend. And it was THEIR idea for once!

"OK I'm in, what do you need?"

They reconvened the next day after Pinkie's shift at the bakery. Twilight used the time in-between to read up on the field and familiarize herself with most of the calculations. Five minutes after Pinkie arrived, the duo was situated in one of the spare rooms that Twilight hadn't found a use for yet. They had dragged in a white board, a large table and some chairs. Pinkie quickly wrote several items on the board.

1. Find an old thing to measure the age of that has not already been measured by a different process. (i.e. carbon dating)
   
2. Determine the age of said subject using archaeomagnetism.
   
3. Check work and summarize data.
   
4. Present scholarly findings to the Equestrian Scientific Committee.

She then put a large check mark next to the first item.

"What are we dating?"

"It's a secret!" Pinkie grinned as Twilight groaned.

"Why am I not surprised..."

"I also don't have it physically." Another groan was Twilight's response as she rubbed her temples.

"How are we supposed to measure its age, then, if we don't have it and I don't know what it is?"

"By measuring everything else around it, silly!"

A purple eyebrow rose. "And how is that supposed to work?"

"Because a measurement was, indirectly, taken of our subject some time ago. However, it was taken before most of the math for this field existed, so nopony ever applied it to the math once it DID exist. So all we have to do is to measure a variety of artifacts until we find one with a similar reading to that of our subject."

Twilight's other eyebrow joined the first, changing a look of incredulity to one of surprise and intrigue.

"Why not just apply the math to that measurement, then?"

"Well, I have a feeling that it's older than most artifacts we have. So the best we could do is a rough estimate of a certain age or older, unless we manage to find an item that predates our subject."

"So you're suggesting that we test a bunch of artifacts in order to make a time-map of where the magnetic pole was at various points in history, and then use that to approximate how old our mystery subject is."

"Yuppers! See, this isn't the most popular way of dating old stuff. From what I've read, ponies usually already have an idea of how old something is before they get archaeomagnetistical about it. Things like carbon dating and records of ownership are used to check their work, essentially. The results can then be used to help determine the age of something that we don't originally know.

Like... we know when Princess Platinum lived, mostly. We have her crown, which was said to have been made five generations before, or something. We have records that detail when each member of the Platinum line came into power and inherited the crown from their parent. Using that, we have a rough date-range of when the crown was likely forged.

After we test it, we'll then have a reading of where the magnetic pole was at that point in time and how strong it was. If our subject has a different position or strength, it could be younger or older than the Platinum Crown. If it has a different measurement than something a bit younger than the crown, it could be younger still or even older than them both!"

Twilight stared at her like she just grew a second head.

"Or..." Pinkie rubs her leg, looking bashfully away, "...at least that's what I've read."

"How much research did you do before you asked for my help?"

"A bit... a bunch of it went over my head though."

Twilight sat back, mind racing. Pinkie was astonishingly correct, as far as she could tell. Her reasoning was frightfully sound. This could actually work. If only she would reveal what the mystery object is.

"This is quite an undertaking, Pinkie. We won't finish with this within a week. Are you sure you don't want to find a different way to use this word?"

"It's OK, the other one took a little longer too. That's just the price I'm willing to pay for quality antics. Plus, it sounds kinda fun. It's a lot of math, but so is baking. This math is just different."

"And you still won't tell me what exactly it is we're trying to get the age of?"

"You'll find out at the same time as everyone else, when we present our findings."

Twilight took a deep breath, mentally preparing herself for the road ahead.

"OK Pinkie. Let's do this. I'll start drafting research requests for the Canterlot archives. Start making a list of any artifacts you think we should test. We've got a lot of work ahead of us."

"Why did you do it, Pinkie?" The harmonica fell silent as Twilight walked down the row of cells, one of the few visitors Pinkie had received since she had been imprisoned. "This could have all been avoided if you just told me your plan from the beginning. I could have stopped this."

Pinkie remained silent.

"No, you just had to finish what you started, didn't you? And now it's landed you here. Are you happy now? Are you satisfied?"

Pinkie regarded her friend with an unreadable expression, idly turning the harmonica over and over in her hooves.

With unwavering certainty, she replied. "Yes."

Author's Note

Here, take it. The sequel I craved to make and at least one of you hoped for.