Over the past few weeks, we’ve explored a variety of topics relating to the part of a watch that most people notice first: the dial. 
 
We looked at  how they are made, some of the most common features, and this week we will explore some of the technical features of dials that turn them into tool watches. 

SUB-SECONDS AND THE ROLEX PRINCE – THE DOCTOR’S WATCH

The earliest additional technical function on a watch, other than telling the hours and minutes, was the sub-seconds. These are most commonly displayed as a small sub-dial at the 6’oclock position. A sub-seconds function simply tracks the 60 seconds of a minute. 
 
It seems simple, but counting seconds is a very important aspect of a watch. The first watch that popularised the sub-seconds function was the Rolex Prince. This wasn’t a tool watch in a traditional sense – it wasn’t dust, or water-proof like the oyster. However, it did become a popular tool watch for doctors, who used the sub-seconds dial to measure lots of vital signs for patients, including heart-rate. 

Vintage Rolex Prince - with large sub-seconds dial

THE PULSOMETER – FOR MEASURING HEART-RATES

Many brands wanted to copy Rolex’s success at attracting customers from the wealthy medical profession, and started to release watches specifically targeting this group. To do so, they had to include functionality that would be useful for doctors. The pulsometer was one such function. 
 
A pulsometer is a scale painted on the dial which is used to calculate heart-rate. The doctor starts the stopwatch and counts 15 or 30 heartbeats, whichever the watch is calibrated for, and then stops the stopwatch. The seconds hand points at the heart-rate on the scale. The Longines 13ZN is an early example of this watch, and started a long history of Longines making watch dials with tools on them for professionals. 

Longines 13ZN with Pulsometer

SLIDE-RULE WATCHES – WHAT ARE THEY FOR AND WHY DO PILOTS LOVE THE BREITLING NAVITIMER?

Another useful function that you might see on tool watches is a slide rule. A slide rule is an old-fashioned mathematical calculator. This function was first put onto watches in the 1940’s, and whilst not the first watch to be offered with a slide rule, the Breitling Navitimer quickly became the most popular. In fact, Breitling still make the Navitimer to this day. 

There are two parts to a slide rule. The first is fixed markings around the outside of the dial – these markings are usually printed onto to the dial. The second is a movable bezel which also has numbers printed onto it. By aligning the two rings of numbers, the wearer can perform a variety of calculations, such as divisions and multiplications. This excellent article explains how to perform those calculations. These watches are often worn by pilots, who use them to calculate fuel consumption and speed and distance of ascent and descent.

Some watches also combine a a slide rule with a chronograph, which gives you a tachymeter function. This is a tool for calculating speed. You can learn more about tachymeters in one of our recent blog posts, here.

Breitling Navitimer with slide rule. The numbers printed on the black dial are fixed, and the wearer can rotate the numbers on the white bezel to perform calculations.

THE MOST COMPLICATED MODERN TOOL WATCHES

Modern tool watches have lots of different technical functions. These functions can be performed by digital and automatic watches. 
 
For example, world timers are becoming more common. This function allows you to tell the time in many different cities and times zones, at the same time. This function can be found on watches at many different price points. At the very high-end, Audemars Piguet have made a world timer with a perpetual calendar which sells for around £30,000. Citizen make a watch with the same world time and perpetual calendar functions for £300. Many Casio g-shock watches can be bought with the same functions for less than £100.

A general principle with additional functions on automatic watches is that the more you add, the more expensive the watch is. For example, the watch that Patek Philippe make with the most additional functions (complications) on the dial is the Grandmaster Chime. Other than tell the time, it can do 20 different things, such as display the year, a second time zone, adjust for leap years and chime upon command. One sold recently for $31m.  

If you want your watch to do lots of different things at a much more affordable price, digital watches, such as the Casio G-Shock range offer a long list of functionality at competitive prices. 

The Casio G-Shock GBX100-2 is a watch targeted at surfers, but is equally useful for fisherman and sailors. Some of the extensive list of additional features that are displayed on the digital dial include: tide Graph, moon Data, high tide and low tide times, and sunrise and sunset times. All of these functions help the wearer to understand sea conditions. Additionally, it includes functions to help with training, and can measure: distance, speed, pace and lap times.  It’s a truly versatile watch.

We at The Watch Collectors’ Club do not have a favourite function, style of dial or even favourite type of watch. We love exploring all kinds of watch and we enjoy exploring the huge range of functions across the watch world. Join us to learn more by following us on Instagram, Facebook or LinkedIn.