Fitting how fate can intervene. In so many ways, Selleck was born to play the role of Thomas Magnum, the Aloha shirt-wearing private investigator operating out of a lush estate in sunny Oahu. His wavy hair, imposing build, and absolutely unparalleled mustache were pillars of 1980’s style. Selleck remains, in many ways, the poster boy for the era.

Magnum had everything at his disposal, from the lavish pad to the choice ride – that red Ferrari 308 – plus his signature Detroit Tigers baseball cap, and of course, his watch. Thomas Magnum was a watch guy, and his watch was the Rolex Pepsi GMT-Master 16750.

Over time, this has undeniably become the symbolic Magnum watch, but it wasn’t always the one on his wrist. In fact, it didn’t appear until the show’s fourth season. He spent much of the first few seasons wearing a Chronosport Sea Quartz 30, which, as Jason Heaton describes it, is “a burly 42-millimeter dive watch with a bright dial and tropic rubber strap.” For the Seiko heads out there, Magnum even occasionally wore a Seiko SQ Quartz diver with a red and blue bezel – you know, for the times he needed a more dive-ready Pepsi watch.

So why is the GMT-Master the perfect Magnum, P.I. watch? For one, it is a watch that matches capability and rugged charm with a bit of whimsy and color. It’s a 100m water-resistant dual-time watch on a steel bracelet, so it’ll hold up well in the surf spray while tracking time back on the mainland. It’s the epitome of a tool watch, but the red and blue keep things from getting too serious. Because no matter how much ass Magnum kicked, he did it with a smile.

Focusing in on the watch for a moment, there’s been some kerfuffle as to what reference GMT-Master Magnum wore. For years, word on the street was a 1675 – the classic matte dial variant produced from 1959 to 1980. With a bit of investigation and some direction on where to look, we can say with confidence that it was in fact a reference 16750.  This was the successor model to the 1675, produced from 1980 to 1988 – matching the series’ run to the very year. Coincidence? (Well, probably).

Two details that illustrate why this is a GMT-Master 16750: The crown guards and the order of the dial hands. As Jon Bues and Eric Wind pointed out in the Reference Points on the GMT-Master, the 16750 has the 24-hour hand positioned between the hour and minute hand. On the 1675, that 24-hour hand is on the bottom i.e. closest to the dial. Next, the 16750 has unique crown guards (in the matte dial variants at least) that differ greatly from any other GMT-Master reference. They are significantly taller and rise above the crown. On the 1675, the crown takes a more prominent position and the crown guards are much shorter.

The “Magnum P.I.” GMT-Master 16750 was one of the earlier iterations in the reference’s seven-year run, featuring a matte dial and painted markers. This would quickly be replaced – forever (sadly) – by a gloss dial and applied markers with white-gold surrounds.

The 16750 is a far more versatile watch, functionally speaking, than its predecessor. First, the water resistance is 100m compared to 50m. Secondly, the 16750 is the first GMT-Master to feature a quick-set date function. Magnum doesn’t have time to spin the hands endlessly on his watch to change the date. He’s undoubtedly a quick-set guy.

So it’s becoming more clear why this is the perfect watch for Magnum, but there’s one reason that rises above all others: It was his father’s watch. That’s right, in the show’s canon, the Magnum P.I. Rolex GMT wasn’t just a watch, it was an heirloom, a keepsake, a memento from Magnum’s late father.

In a flashback in the fourth season’s premiere episode, a young Thomas Magnum swims in the ocean with his dad. While in the water, his father takes a moment to reference his watch while timing his son’s swimming. The camera fixes tightly on the GMT 16750 with its matte dial, Pepsi bezel, and bright white markers. No patina on this one, folks.

The episode also sadly features his father’s death, showing young Thomas performing a military salute à la JFK Jr. at the funeral with that GMT-Master dangling from his child-sized wrists.

Of course, there’s a bit of suspension of disbelief necessary here. If you do the math (and don’t because it will frustrate you and hurt your brain), the 16750 would not yet have been manufactured when Magnum was a young boy. It first launched the same year the show began, so…you know, it didn’t exist. But this is television, and the normal laws of time don’t apply.

On its own, the GMT-Master 16750 is about as quintessentially a GMT-Master (and Rolex steel sports watch) as they come. Nowadays, with values rising on this model, you’ll find versions with faded bezels that have turned all manner of funky colors, and heavy patina on the markers. In the show, it exists forever in its proper era, frozen in time – helping Magnum beat the bad guys, and close the case.

Selleck has since gone on the record about this watch (though he did refer to it as 1675), admitting that of the many cool props on the show, Ferrari included, it was the Pepsi GMT that he kept. Speaking to the FHH, he noted:

“I’ve always loved that watch. It was the perfect match for Magnum. It’s a watch that likes action, and believe me I know what I’m talking about. I’ve had my fair share of ‘sport’ watches but never one as tough as the Rolex. It’s been underwater, buried in sand, taken I don’t know how many knocks, and never a problem. It’s called the Pepsi because the bezel colors are the same as the Pepsi logo. Personally, I thought the red went well with the Ferrari and the blue matched Hawaii’s lagoons and sky.”

So there you have it. The perfect Magnum P.I. watch is the one Magnum decided to keep for himself.