How to Use a Navitimer Slide Rule (and Why Pilots Loved It)
A plain-English walkthrough of the most famous bezel in watchmaking: what every marker means, five calculations you can do today, and why it earned a place in cockpits and in orbit.
The Pilot's Watch That Went to Space With a 24-Hour Dial
On May 24, 1962, astronaut Scott Carpenter orbited the Earth three times aboard Aurora 7 wearing a Breitling. He had seen pilots wearing the Navitimer and asked Breitling for one change: a 24-hour dial, because in orbit there is no simple way to tell noon from midnight. That watch became the Navitimer Cosmonaute.
Europa Star's account of the Cosmonaute story covers how Breitling brought Carpenter's original watch out for public view for the first time on the mission's 60th anniversary. It was the same year NASA's Manned Spacecraft Center began its move to Houston, the program you can still explore at Space Center Houston.
But Carpenter wanted the Navitimer for the same reason pilots did: the bezel. That ring of tiny numbers is not decoration. It is a working circular computer, and once you know three markers, you can use it in about five minutes.
A Navitimer slide rule is a logarithmic calculator built into the bezel: you rotate the outer scale against the fixed inner scale and read the result where the numbers line up. Use the red 10 unit index for multiplication and division, and the 60 hour index at 12 o'clock for speed, time, and fuel. You supply the decimal point yourself.
What the Navitimer Slide Rule Actually Is
Breitling first put a slide rule bezel on the Chronomat in the early 1940s. In 1952, working with the Aircraft Owners and Pilots Association (AOPA), the company refined the idea for aviation and launched the Navitimer, a chronograph that doubled as a flight computer. The Hour Glass collector's guide walks through how the line evolved from there.
The scales are logarithmic, not linear. That is what lets two rotating rings multiply and divide: sliding one scale against the other adds distances, and on a log scale adding distances multiplies numbers. The trade-off is that the bezel never shows a decimal point. A reading of 24 could mean 2.4, 24, or 240, and common sense tells you which.
The Markers You Need to Know
Every Breitling Navitimer bezel works the same way, even though printing and colors vary by generation. Learn these markers and the rest is lining up numbers.
| Marker | Where It Sits | What It Does |
|---|---|---|
| Outer scale | On the rotating bezel | Holds your first value and shows the answer |
| Inner scale | Fixed, just inside the bezel | Holds your second value, usually time in minutes |
| Red 10 (unit index) | Inner scale, a little past 2 o'clock | Reference point for multiplication and division |
| 60 hour index (often marked MPH) | Inner scale at 12 o'clock | Reference point for anything "per hour": speed, fuel burn, travel time |
| STAT, NAUT, KM | Small labeled marks on the inner scale | Convert between statute miles, nautical miles, and kilometers |
How to Use a Slide Rule Watch, Step by Step
Grab your Navitimer (or picture one) and try these in order. Each one builds on the last, and all five use only the markers in the table above.
The examples follow the same logic used in The 1916 Company's pilot's guide and Watchmaster's slide rule explainer, both worth reading if you want more practice problems.
1. Multiply
To work out 12 x 3, rotate the bezel until 12 on the outer scale sits over the red 10. Find 3 (printed as 30) on the inner scale and read the number above it on the outer scale: 36.
2. Divide
To work out 40 divided by 5, place 40 on the outer scale over 5 (printed as 50) on the inner scale, then read the number above the red 10: 8. That is also a 20% tip on a $40 check.
3. Average Speed
If you covered 80 kilometers in 20 minutes, set 80 on the outer scale over 20 on the inner scale. Read the number above the 60 hour index: 240, so 240 km/h. The same method works in miles or knots.
4. Fuel Burn
If an aircraft burns 20 gallons per hour, set 20 on the outer scale over the 60 hour index. For a three-hour flight, find 180 minutes (printed as 18) on the inner scale and read the outer scale: 60 gallons.
5. Convert Miles to Kilometers
Set the distance on the outer scale over the STAT mark (or NAUT for nautical miles), then read the kilometer figure on the outer scale above the KM mark. It is the fastest way to turn a road sign or chart distance into the unit you think in.
Estimate First
Decide roughly how big the answer should be before you turn the bezel. The scale gives you digits, and common sense places the decimal point.
Read Between the Marks
Tick marks get crowded at higher numbers. Estimate halfway points and read in good light, and your answers will land within a few percent.
Turn Gently
The Navitimer bezel rotates in both directions. Use a light, even touch and never force it, since a stiff or gritty bezel is a service item.
Practice on Everyday Math
Tips, gas mileage, and recipe conversions are perfect practice. A week of small problems and the bezel becomes second nature.
Why Pilots Loved the Breitling Navitimer Bezel
Before electronic flight computers, pilots solved time, speed, distance, and fuel problems on handheld circular computers. The Breitling Navitimer bezel put that same logic on the wrist and paired it with a chronograph, so a pilot could time a leg of a flight and calculate ground speed without letting go of the controls for long.
AOPA members adopted it, the AOPA wings appeared on early dials, and the Navitimer became the pilot's chronograph. Crown and Caliber's Navitimer guide explains how Breitling's key move was combining the slide rule with the chronograph. Today pilots use digital avionics, but the bezel still works exactly as it did in 1952, which is a large part of its appeal.
Buying a Pre-Owned Navitimer in Houston: What to Check
If this guide has you shopping for a pre-owned Navitimer in Houston, the slide rule is the first place to look. It tells you a lot about how the watch has been treated.
- Bezel action: it should turn smoothly both ways without grinding, slipping, or wobble.
- Printing: the scale numbers should be crisp and even. Faded or smudged printing can signal a replacement part or heavy wear.
- Chronograph: start, stop, and reset should be clean, with hands returning exactly to zero.
- Reference and movement: modern Navitimer B01 models use Breitling's in-house calibre, while older generations used other movements. Know which one you are paying for.
- Size: current Navitimers come in several case sizes, and a 46mm wears very differently from a 41mm. Try them on.
What Buying a Navitimer Looks Like With Us
At Houston Time Pieces, you book a private appointment at our North Loop West office and we lay out Navitimer options side by side, including Cosmonaute and 24-hour versions when we have them. Every watch is authenticated, the bezel and chronograph are tested, and condition is described honestly. If we do not have the reference you want, we source it. We will even walk you through the slide rule before you leave.
Clients come from River Oaks, Memorial, the Galleria and Uptown, the Heights, Katy, Sugar Land, The Woodlands, Pearland, Cypress, and Clear Lake, not far from where NASA's astronauts train today. See our full approach on the Breitling buy, sell, and trade page, start with our buy a watch in Houston page, or, if you are upgrading, learn how to sell your watch in Houston and put the value toward a Navitimer.
Frequently Asked Questions
Rotate the outer bezel to line up a known value against the fixed inner scale, then read the answer elsewhere on the scale. For multiplication and division you work against the red 10 unit index, and for speed, time, and fuel you work against the hour index marked 60 at 12 o'clock. You always place the decimal point yourself.
Yes. The Breitling Navitimer bezel is a working circular slide rule that multiplies, divides, and converts units without batteries or signal. Pilots now rely on electronic avionics, but owners still use it for quick checks on speed, fuel, travel time, currency, and even restaurant tips.
The red 10 on the inner scale is the unit index. It is the reference point for multiplication and division: set the first number above it to multiply, or read the result above it after dividing. On most modern Navitimers it sits a little past the 2 o'clock position.
The Navitimer Cosmonaute is the version of the Navitimer with a 24-hour dial, created at the request of astronaut Scott Carpenter so he could tell day from night in orbit. He wore it aboard Aurora 7 on May 24, 1962, and Breitling has revisited the design in several modern editions.
Check that the bezel turns smoothly in both directions and that the slide rule printing is crisp, confirm the chronograph starts, stops, and resets correctly, and verify the reference and movement. Houston Time Pieces authenticates every pre-owned Navitimer in person at 2050 North Loop W, Suite 116, Houston, TX 77018.
Yes. Houston Time Pieces accepts trade-ins across more than 25 luxury brands and applies the appraised value directly toward a Navitimer from inventory or one sourced for you. You pay only the difference, and the valuation and trade happen in one appointment. Call (281) 584-3032 to book.
Buy, Sell, or Trade With Houston Time Pieces
Looking for a specific Navitimer, or want an honest opinion on one you found? Book a private consultation or get a fast, no-obligation offer. Every timepiece is inspected for authenticity, condition, and long-term value, with secure nationwide shipping.