Numeric Scales on Watches Matter 

A lot of watches have numeric scales on their dials, but we need them?

Or, mental math is a bad way to define watch functionality 

When I was a kid, growing up in the midwestern United States and visiting family in Nebraska – where giant thunderstorms rolling across the prairie isn’t just a Laura Ingalls-Wilder story, but instead a real experience – a family member of mine taught me how to calculate how far away lightning was. You, dear reader, may be familiar with this: count the number of seconds between seeing lightning and hearing thunder, divide by five, and that’s the number of miles between you and the lightning (the denominator is different for kilometers, but the same concept applies).  

Chronographs support this too, or some do. If your chronograph has a telemeter scale visible to you, you can perform this same calculation, without mental math. This is just one example of the core idea of this post: scales on watches matter.  


In user interface design (yeah, computer-based user interfaces), there is a set of 10 heuristics (rules of thumb) that are used to identify usability problems. Trust me, I’m a doctor. I want to focus on two of these heuristics here because they explain why scales are so important: visibility, and recognition, not recall.  

In user experience evaluation, the visibility heuristic says that the user of a system should always be able to see the status (in UX, of a computer system). Similarly, the recognition, not recall heuristic says that the user should be able to recognize what they’re supposed to do, not have to remember it based on prior experience.  

In watches, I’d argue that these two heuristics help explain why the numeric scales on watches are so important. Take a dive bezel. The whole point of a dive bezel is that it serves as an elapsed time reference so that a diver can time how long they’ve been underwater, to make sure they don’t get the bends in their ascent (notably: not how much air is left). Quite literally, the premise is to enable a diver to visually understand the state of the dive and recognize (not recall) how long they’ve been underwater (referred to as bottom time). The rotating bezel mechanism enables the scale to change, reference point, but without the scale itself, you’d just have a fidget toy.  

The value of a dive bezel, to a watch-wearer (even if one does not dive), is pretty obvious – timing how long your laundry has been in the washer using a reference point on a bezel is a lot easier than remembering when you started your laundry and doing mental math. But! Lest you get the wrong idea, this post isn’t only about dive bezels. No no no, dive bezels are just the proverbial BEER BAIT FOOD sign on the proverbial gas station.  

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Photo courtesy of Ken Lund

Tracking Three Timezones 

Let’s take another example that really grinds my gears (pun intended): “With a Rolex GMT Master II, you can track three timezones”. No. You. Can’t. The three-timezone claim assumes you have your standard 12-hour timezone, you have a 24-hour timezone as tracked by the 24-hour hand, and you have an external bezel that you can use to offset against the 24-hour hand.  

But importantly: as soon as you turn that external bezel, you have lost all reference you previously had for the 24-hour hand! You have either changed the state of the system, or you have to recall (not recognize) the reference for the third timezone. To be moderately provocative – if mental math is necessary for tracking three timezones, any watch can track all timezones, because all you need is mental math.  


Notably, some folks do this correctly! Grand Seiko has several GMT watches with a 24-hour scale printed on the chapter ring (excuse me, *rehaut*), *as well as* on an external rotating bezel. That will let you track three timezones! My argument here isn’t that GMTs can’t track three timezones, but instead GMTs with only one 24-hour scale can’t track three timezones. 

More Broadly: Scales Matter 

Look, I’m hearing you (cough Will cough) – I don’t hate GMTs. They’re my favorite complication. My point here isn’t about GMTs, it’s that the scales on watches matter. Fundamentally, a lot of what we, as watch enthusiasts, talk about when we talk about tool watches is usability. Tool watches are tools because they facilitate and support a specific task and goal. The usability of these watches allows them to work well and helps people not have to think about the tool.  

The thunderstorm story I told at the top? Nurses do similar mental math to measure a patient’s pulse. A pulsometer scale on a chronograph makes that easier. Is it necessary? No. Is it helpful? I’d venture to say yes. You can compute how fast you’re going based on mile markers and mental math, but a tachymeter scale on a chronograph makes that easier. Sure, you can do mental math to compute three timezones with a GMT hand and a rotating bezel, but it’s easier if you put a 24-hour scale on the chapter ring and an external rotating bezel, as Grand Seiko does in some models.  


Fundamentally, most of us watch enthusiasts know this: it’s why putting a 24-hour scale and then aligning that with a city ring makes a worldtimer. The usability of watch scales is also partially why California dials feel weird to lots of people – changing the way of representing numerals requires recall, not recognition.  

Can “Scales Matter” Go Too Far? 

What’s that, dear reader? Shouldn’t we just put All the Scales on watches? In short? No. Consider the Sinn 900 Multifunktions Chronograph. It will support visibility of system status, but over-stuffing scales massively harm recognition, not recall. It’s not only that the dial is too visually busy (it is), but the busyness on the dial makes it hard to read the watch because it requires you to remember how. 

“This watch is a perfect example of too much information, but if anybody has one for sale, please contact me as I have a friend (with questionable taste) that really wants one.”

User experience principles would suggest that expert users will learn to use this kind of watch and it’ll be an effective tool, but it’s essentially inscrutable to novices. I’ll be the first to tell you: I’ll own being a novice, and I don’t want to do what it takes to be an expert! 

I have now convinced you that scales on watches – and more fundamentally, watch usability – matters! This article is over. Remember: watches are fun, buy what you like. 

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