I loved the island of St. Martin/St. Maarten. St. Martin is the French side, and St. Maarten is the Dutch side. I first discovered it in the late 1970s.

I always stayed on the French side. It was livelier, with a heavy concentration of Canadians and English-speaking Europeans. No matter where you went, whether you were vacationing solo or with someone, you could join a group of fellow vacationers. It became my island of choice for winter vacations.

It wasn’t St. Thomas, with its wild nightly parties. St. Martin was a little more sedate, but there was still nightlife if you could last that long after a full day of swimming and tanning in the hot sun.

On my first trip, I learned that I was getting a little more than four French francs to the dollar. “That’s odd,” I thought.

At our crew hotel in Paris, I could get closer to five francs to the dollar. It was cheaper to buy in Paris and spend in St. Martin.

Buying $200 worth of francs in Paris gave me roughly $50 in extra spending power on the island.

With my airline discounts at the hotels and near-free air travel, that total was enough for several days of sun and fun on the island each month.

On another trip to Paris, some people on my crew introduced me to a Vietnamese street vendor. He knew everyone’s name but mine. Apparently, these crew members were regular customers. He learned my name, and I became part of his in-crowd.

This was not uncommon. We had our preferred vendors wherever we went.

This man sold all types of wares, and this crew was interested only in buying francs. He gave us roughly one extra franc per dollar above the crew hotel’s rate that day. I was still a bit green, and I certainly didn’t understand international finance, but I knew a deal when I saw one. And I didn’t ask any questions. I just loaded up since I often flew the JFK–Paris trip.

One trip, I went into the cockpit for something, and I asked them where they exchanged their dollars in Paris. “The Vietnamese guy,” they said.

“Oh, I just learned about him.”

“Yeah, the money changer.”

“Oh.”

I made a quick exit from the cockpit.

Then, on one trip to St. Martin, I found that the exchange rate suddenly matched the rate in Paris, and I was told they had “harmonized” with the official Paris rate.

The party was over, but it was great while it lasted.

A few years later, I was watching a financial show.

Arbitrage.

So, that’s what they call it.