I’m old enough to have been raised on slide rules. I have a deep fondness for slide rules, the simple beauty of their power. Ok, I was a 60’s nerd too, but by senior year in high school, I had three or four.

I’ve always been intrigued by the idea of a slide rule bezel on a chronograph and have had some close calls with fetching Breitlings over the years. But I never bit.

I’ve noticed that some of these ‘slide rule bezels’ aren’t actually, because the two scales run in oppposite directions from each other. The inner scale increases in a clockwise direction and the outer scale decreases in a clockwise direction.



On the other hand, this is what I would expect from a slide rule bezel.



Why are some of the bezels in the opposite direction? Is there a purpose or a function that they serve that way?

I suspect I’m going to feel stupid once it’s been explained to me, but I guess I’m willing to risk it.

 

You can still multiply with it this way, just align the multiplicands and read the results at the 1 of either bezel. Division is a similar inversion. I don't know what the benefit is or if that's the recommended method or use.

 

Yup. I see what you mean. I’ve never handled one, so I’ve never had the opportunity to manipulate one to figure it out.

Thanks!

Edit: I wonder why I’ve never NEVER seen a reversed slide rule in any other context. Including years of eBay searches...

 

Maybe it’s by application and maybe it’s by age. My anecdotal survey on eBay suggests that only older models have this reversal.



This one is mouth watering, sold on eBay for less than $2.4k


There are Breitling experts here on OF...

 

Google e6b slide rule, it’s slightly different, and modern Brietlings use a normal slide rule. While the Sinn 903 the true Navitimer still uses an e6b.

https://en.m.wikipedia.org/wiki/E6B

 

This will explain all my friend.

Liked the rule of 3 scenario with the pilot and wine


https://journal.hautehorlogerie.org/en/slide-rule-what-is-it-and-how-does-it-work/

 

Damn ... I had slide rules in HS but then my dad got an HP35 and the world changed ... it’s good to remember that prior to that all our tech advancements were built with slide rules. Now I wish I had a breitling to play with while reading the above!

 

Very interesting article. But all the circular slide rules they illustrate are standard orientation, i.e. both scales increase in a clockwise direction. On the older Breitlings, the outer scale decreases in a clockwise direction instead of increasing.

Thanks for this link, but I do know how to use a slide rule. I didn’t see anything that talked about the reversal of the second scale in earlier Breitlings.

Ditto.

The history of this complication is very interesting and I’ve appreciated learning it. I gather that the older Chronomats have this reversal but when they modernized to the Navitimer, the outer scale was corrected to run in the same direction as the inner scale.

But I’m still curious about why this started out as a reversed outer scale when all slide rules, which had been around for over 50 years at the time, have scales that run in the same direction.

Anyone know more?

 

Not necessarily, here are the two sides of the slide-rule I used in college and early working life:




See the relationship between C & CI and D & DI? They are reciprocal scales. CI is often found next to CF, which is C shifted by Pi, to get the reciprocal of Pi quickly.

I have no idea why the Breitlings were reversed though, maybe it's comparable to RPN as used by Hewlett-Packard calculators. It may be faster under some circumstances but being "non-standard" makes its adoption difficult.

 

https://web.archive.org/web/20130719031710/http://sliderulewatches.yvod.com/ is very informative on the history of slide rule watches. The relevant section for why early Breitlings run backwards (with a C and CI scale) implies that it was done for patent reasons: