Reading Time - the Breitling Bezel

Here it is: The long awaited Breitling 'how to' component of our reading time newsletter articles (or at least part one for Breitling). How to use a Breitling bezel, or any other flight type bezel for that matter: We should first start out by defining the points on the bezel and what they mean, so as to ease our understanding of the calculations and how to make them. Firstly, the bezel is technically called a slide rule. Pilots have used them for decades to calculate anything from simple multiplications, to how far to turn the nose of their plane into a crosswind so as not to be pushed off course. Below we can see an actual slide rule (or in this very complicated case, 'flight computer') used in the training of pilots, which was kindly donated to us by a loyal supporter. This is a standard tool across the aviation industry and when Willy Breitling first released his Navitimer in 1952 at the behest of the US Aircraft Owners and Pilots Association, he designed the slide rule to be as similar as possible to the below training tool. This instantly made the watch familiar to the AOPA members and is one of the main reasons the Navitimer is the go-to for pilots worldwide. The slide rule is made up of two rules or tracks, the fixed (inner) and the sliding (outer). The fixed rule or track is on the actual dial, and like the name suggests, does not move. The sliding rule or track is on the bezel itself and is what you rotate to make the calculations. Most pilot watches will also have a tachymeter and then a minute track for the running time, printed inside the two slide rule tracks. When making the calculations below, the only numbers considered are the ones on the two outermost tracks.

Another thing we must understand is that the decimal point is not found on a slide rule. For example the 16 on the outer bezel also represents 0.0016, 0.016, 0.16, 1.6, 160, 1600, 16000 etc. A little bit of common sense is needed here, and will become apparent in the explanations below. The slide rule is also not a linear scale but a logarithmic one. This just means the physical distance on the scale between similar intervals is different, for example the distance between 10 and 20 on the outer ring is much further than between 20 and 30. The best thing to do for practice is make different calculations with your watch and check them with a calculator to gain confidence. First off, let’s start with everybody's favourite calculation: Division. This calculation is fairly easy actually. Let’s say we want to divide 75 by 12. Maybe it's a shared Christmas gift for someone (a little late I know but a good example). Line up 75 on the sliding outer track with 12 on the fixed inner track. The 10 (in red) on the fixed inner track will point to the answer which is 62.5. Now the decimal place dilemma comes into play. We know that 62.5 is much too large an answer for our question. So we mentally slide the decimal place across to either 6.25, or further to 0.625. It’s easy to see that 0.625 is way too small to be the answer, so we stick with 6.25 or $6.25 per person. Percentages? Even easier. Say we want to find 19.8% of 57,500 (keeping in mind a complex calculation like this is difficult to find the exact number as there just isn't enough room on the bezel). We line up 57.5 on the outer sliding bezel with 10 (in red) on the inner fixed track. We then look for 19.8 on the fixed inner track and the answer on the bezel reads a tiny bit under 11.4 which with decimal place adjustment is just under $11,400. A short trip to your iPhone calculator confirms the answer as 11,385. Without moving the bezel, you can see any percentage of 55,700 or 557 or 0.557. You just read from a different number on the inner track to its corresponding number on the outer track, and keep the decimal place dilemma in mind.  Second cab off the rank: Multiplication. Remember your 17 times tables? Absolutely not. But now you've not only got a Breitling Navitimer, you know how to use it. Slide your bezel so that 17 on the outer track is lined up with 10 (in red) on the fixed inner track. Now the result for any fixed number (inner track) multiplied by 17, is displayed on the outer track. For example, 17 x 25 = 42.5. But we know that number is much too small to be the correct answer, so we move the decimal point over to either 425 or 4,250 or 42,500. A simple calculation like 20 x 25 = 500 makes it easy to confirm the answer is indeed 425. For the case where the numbers do not line up exactly, either an approximation can be made, or you can just mentally work around it. For example 17 x 26 = looks like maybe 44.1 or 44.2 (441 or 442) by reading off the bezel. Alternatively, you can just calculate 17 x 20 and 17 x 6 (6 being the MPH marker at the top of the dial, which reads as 10.2 but is actually 102) as they are easier to see. Adding these gives us 340 + 102 = 442. Or you can just look around the bezel for the closest whole number even multiplication and add or subtract the rest in your head. I do apologise again if these explanations are getting a little too confusing to understand. There are so many more calculations that can be made with the sliding bezel but for this newsletter I will leave you with these two most common everyday calculations. We will get back into Breitling soon. Andrew