# Caliper Slide Rule Watch MKII

I have a long-standing fascination with old calculating devices. Some years ago, I learned how to use a slide rule. The elegance and power of such a simple design is almost magical. How can sliding two scales against each other produce so much mathematical power?

Without getting too technical, a slide rule adds and subtracts logarithms which, it turns out, is the same as multiplication and division.

Is this just a historic curiosity? Why would you want to use a slide rule? And why would you want one on your watch?

Here’s why: a slide rule is faster than a calculator when you need to multiply or divide many numbers by the same factor. This would be the case for units conversion or currency conversion. Set a slide rule to a particular factor, and you can read back and forth across the dial to get results for any value almost instantly. Doesn’t that sound like something useful to have on your wrist?

Of course, slide rules have appeared on watches for a long time. Most watch slide rules are based on a specific type of slide rule  designed for the needs of pilots. A pilot watch layout typically places 6.0 on the log scales at the 12 of the watch. Handy for navigational calculations but confusing for everyone else.

My goal has been to make a slide rule watch that focuses on clarity and legibility of the slide rule and therefore maximizes its utility.  Here are some aspects of the design that support this goal:

The Slide rule index is at 12 – at the top of the dial. This is the conventional ‘starting point’ on a watch dial.

We do not show any conversion factors on the dial. This reduces clutter and lets you focus on the setting that you have selected.  We have a large number of conversion factors on the back of the case that you can easily refer to, and memorize over time!

The case back is steel and finished with a circular brush pattern.

In this version, we have used a quartz movement with a battery that will last several years (The original caliper Slide View was mechanical). No winding, no setting. When you want to wear this watch, it’s ready to go.

I’ve been consistent with the major and minor markings on the logarithmic scale. Often, slide rule scales add more detailed markings where there is room. I think one consistent set of major and minor markings better illustrate the true nature of the log scale and allows you to better see their orientation at a glance.

I’ve placed the rotating bezel inside the case. This allows the scales to be as close as possible which makes calculations more accurate.

I’ve kept the face of the watch very simple. The hours are show with applied markers but without numbers.

The slide rule is controlled by the crown at the 4 position. I’ve chosen this location because it allows adjustment of the slide rule scale without having your fingers in the way.

To ensure we that you can make full use of the slide rule function, we’re including instructions, examples and a practice slide rule device:

## Caliper Slide View MKII Models

The Caliper Slide View MKII BST

The Caliper Slide View MKII OST

The Caliper Slide View MKII OBL

Specifications:

• Black Dial
• Orange second hand and details
• Black IP Steel Case (316L Steel)
• Mineral crystal scratch resistant glass
• Water resistant to five atmospheres
• Swiss Ronda quartz movement with five-year battery life
• 43 mm case diameter, 10.5mm height, 22mm band width
• Super Luminova lume
• Leather strap with orange stitching and quick release pins