Par Weber Coefficient Watch Review - True American Innovation in the Watch Industry

Par Weber Coefficient Watch Review - True American Innovation in the Watch Industry

The story of Par Weber watches starts in an unlikely place. In 2018, then new father Jon Weber found himself frustrated in the middle of the night for more than the obvious reasons. As a father of a two-year-old myself, I can vividly remember wondering how many minutes it had been since the last time I woke up. I found myself desperately bargaining with the clock, thinking "can I squeeze in three hours of sleep before I have to get up for work?"

Jon found that his existing watches were letting him down at this critical time, and set out to find a solution. Even if it starts the night fully "charged," lume only lasts so long. Tritium will dim as its half-lives pass, plus the tubes can be difficult to see if you are not in total darkness. G-Shock and Timex have bright backlight, but they require to you press a button or tilt your wrist to get a few seconds of illumination. Risky moves when holding a baby that you are trying to will to sleep.

Situations like this is where Par Weber's watch promises to shine (pun intended..I said I'm a dad).

The Chicago-based company worked with US-based manufacturing partners to develop a new (and patent-pending) system of illumunators called Enduro-Lume. It promises continuous illumination, providing the best possible legibility during the day as well as throughout the night. Enduro-Lume is made in the United States of 80% U.S. content. It is then combined with a Swiss quartz movement, with final assembly in Switzerland. Best of all, the lume battery is intended to last as long as the battery powering the movement (3+ years). No carrying around chargers, or frequent opening of the case is required.

After six months and 257 prototypes, the Coefficient is available for purchase. Jon was gracious enough to send me one to give me a chance to check out the technology.

According to Par Weber "these emitters are calibrated to project a wavelength optimized for how dark-adjusted eyes perceive light." My fear was that this is marketing speak for "it's really dim." In order to power twelve LEDs constantly for multiple years, a very low amount of current must be used. Sure, Enduro-Lume looks bright in the marketing photos, but that is easy to achieve with adjustments in camera settings.

The watch made big promises, so I was excited to see it in person. Does Enduro-Lume live up to its promises, or is it a gimmick? Keep reading to find out!

First Impressions

As you might expect, I had the lights on when I opened the box, so the first thing that I noticed about the Coefficient was the all-black stainless steel case.

Par Weber Coefficient Review Eundro-Lume Strap Box

The watch arrives well-padded in a large box. A springbar tool and extra springbars hide under the green single-pass nylon strap.

Par Weber developed the watch with a strict form-follows-function philosophy, and it shows. Rather than build a watch as a homage to a vintage model, or to fit a specific style aesthetic of a type of customer, every part of the Coefficient was designed to do the best possible job at being a watch.

Par Weber Coefficient Review Eundro-Lume

Form following function.

This shows in the fully matte-black case, and stark white dial. The Coefficient is a tool watch if there ever was one, but there is something fun and refreshing about strapping it on. Think of it as a Land Rover Defender for your wrist. It's functional design is what makes it look cool.


Normally I discuss the dial in the middle of a review, but since this is where the Coefficient's magic happens, I'll jump right into it.

Par Weber Coefficient Review Eundro-Lume

A dial designed around legibility.

At first glance, the dial appears to be a plain white disc, but it actually has a transparent top surface. The requisite logos, as well as the hour markers are painted on, making them appear to float above the dial. The large Par Weber logo and a triangle at twelve are painted in red and help you to find the top of the dial when reading time at a glace. Six and nine are Arabic numerals, and the remaining hours are small dots, all in black.

The rectangular date aperture is at three, with a white background matching the dial. Rather than many lines of text, the dial is refreshingly devoid of...umm...superlatives (that was for the Rolex owners. Last dad joke, I promise).

Par Weber Coefficient Review Eundro-Lume endurolume dial

Markers and logos printed on a transparent top layer appear to float.

Rather than pure white, the dial has an eggshell color and texture. The side effect of designing it to efficiently use every ray of light generated by the LEDs, is that any small amount of ambient light also brightens the dial. The result is supreme legibility even in transient situations, such as walking between bright and dark rooms.

Par Weber Coefficient Review Eundro-Lume endurolume dial

It's difficult to capture in photos, but the dial has an eggshell finish.

The dial has no minute markings, but a deep, sloped chapter ring features white over black (red at twelve) marks for hours and minutes.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The chapter ring hides a secret.

By now, maybe you've noticed that the transparent top surface of the dial creates what looks like a small gap below the chapter ring. This gap is where Enduro-Lume does its thing. Twelve small LEDs sit under said chapter ring, constantly illuminating the dial through this gap with a cool white glow! As they are lined up with the hour markers, the illumination appears to come from underneath the black dots and numerals.

Par Weber Coefficient Review Eundro-Lume endurolume dial glowing lume shot

The transparent top layer of the dial creates the appearance of a gap. This is where the magic happens.

Enduro-Lume is not blazing like fully charged Superluminva when the lights go out, but is much brighter than I expected, and brighter than tritium, or lume that wasn't very recently exposed to sunlight. There is never a situation where reading the time requires your eyes to adjust. This feature is the real deal!

I would estimate that it is about 25% as bright as the backlight on my positive LCD G-Shock Mudman. That might not sound that bright, but consider how annoying that a G-Shock would be if lit up all the time. Enduro-Lume is just the right amount of brightness to provide legibility without being too distracting (plus its display is much higher contrast than the G).

Par Weber Coefficient Review Eundro-Lume endurolume dial glowing lume shot at night

Twelve small LEDs transmit light across the dial.

You can tell that significant care went into the selection of the LEDs, and design of the optical diffuser, as all of the light sources produce uniform amounts of light. I imagine requires significant quality control, especially when operating the LEDs at such a low current.

Par Weber Coefficient Review Eundro-Lume endurolume dial

Enduro-Lume's LED module (white) and battery module (red). The movement sandwiches in the middle.
Photo courtesy of Par Weber.

If I had to pick one complaint about the dial, it's that it is a bit small compared to the case. I talked to Jon, and this is a result of packaging the LEDs and supporting hardware while still having a watch that is a wearable size. The legibility is still great, and the side benefit of this is that the date window location looks correct (versus a bigger size, which would have the date floating lost in the middle of the dial). This also places the date next to the three o'clock illuminator, allowing the date to be read in the dark.


What good is a legible, illuminated dial if the hands are difficult to read? One of the design constraints of the Coefficient was hour and minute hands that are easily identifiable. Their solution is a wide hour hand with a skeletonized triangle at the tip (like a thicker Omega broad arrow), and a slightly thinner, but very long minute hand reaching to the edge of the dial.

The hands are painted in matte black, and of course have no lume. At night, they are identified by the shadow they create over the dial.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The hands are designed around legibility too.

The seconds hand is a simple stick hand with a rectangular counter-balance.

Par Weber Coefficient Review Eundro-Lume endurolume dial

A broad arrow hour hand differentiates it from the minute hand.

The hands provide the great legibility intended. They are matte black, and appear to be paper-thin. In certain conditions, it gives the appearance that the time is displayed on an LCD screen rather than with physical hands.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The hands are paper thin and matte black. Combined with the off-white dial, the time looks as if it is being displayed on an LCD screen in the right light.


Continuing with the "form second" theme, the Coefficient's case is designed to be functional and comfortable. It sits at 43mm in diameter (48mm lug-to-lug), and 14mm thick, with a manageable weight of 95 grams.

Par Weber Coefficient Review Eundro-Lume endurolume on wrist

At 43mm, the Coefficient is sized like many dive watches.

It's not small, but the dimensions are typical of a dive watch, making it very wearable. The difference here is that the large case is actually used to package the Enduro-Lume system. Many watches are big only for styling reasons. They have a small movement with a large case and spacer filling the gap.

Par Weber Coefficient Review Eundro-Lume endurolume dial wearing

14mm thickness is also typical of a dive watch. Yet this one houses a second battery and additional hardware with a movement sandwiched in between.

Helping that wearability are the 20mm spaced lugs mounted low on the case. Based on the photos, I was afraid that this would make the watch top-heavy, but that is not the case. It felt tied down to my wrist at all times.

Par Weber Coefficient Review Eundro-Lume endurolume lug drilled lugs

The lugs are mounted very low on the case for improved stability on the wrist.

Rather than chase specs that will not benefit the typical owner, Par Weber sought to make the Coefficient stand up to actual conditions it would experience. Thus is is not a dive watch, and is rated for a completely sufficient 100m water resistance. It should be able to stand up to anything an actual user will encounter.

Par Weber Coefficient Review Eundro-Lume endurolume dial

Matte black PVD coats the entire watch.

The entire 316L stainles steel case is PVD-coated in matte black. It does show fingerprints easily, but it's quickly wiped off. PVD is supposed to be fairly durable, but this is a watch that will look even cooler after it picks up some dings and wear marks.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The tool watch appearance means the Coefficient will look really cool after some abuse.

The screw-down case-back is machined around the edge with a unique polished center. It features laser engraved information such as the model number of both types of batteries, and lug-width. Again, no advertisements, just information useful to the owner.

Par Weber Coefficient Review Eundro-Lume endurolume caseback case-back case back

The case-back features useful information such as the battery types.

Unlike on a lot of watches, the case-back extends to the extreme edges of the case. This is to allow the installation of the Enduro-Lume system.

Par Weber Coefficient Review Eundro-Lume endurolume battery movement

Enduro-Lume's battery module.
Photo courtesy of Par Weber.

I love the functional design, and the fact that Par Weber did not style this watch after any existing watch. The utilitarian case is the perfect envelope to showcase this new and exclusive system.


The bezel of the Coefficient is inspired by the aperture ring of a camera lens, which is of course designed to be easy to grip. The ridges around the edge are a similar size, and it protrudes just slightly from the edge of the case as an aperture ring does.

The top surface is very wide compared to the size of the dial because the Enduro-Lume system is packaged underneath. The fact that there is no bezel insert also makes it look wider than other watches. I imagine the one piece design adds some durability, as there is no insert to possibly fall out.

Par Weber Coefficient Review Eundro-Lume endurolume case side

The bezel grip is inspired by the aperture ring on a camera lens. It overhangs the case slightly, making it easy to grip.

The bezel features 120 clicks. Since this is not a dive watch, it is bidirectional, making it more convenient to use and reset to zero. The click feeling is the bezel action is really nice. Not as precise as something like a Tudor Pelagos, but more crisp and positive than typical watches in this price range. Not only does it use a font like an aperture ring, it has a similar feeling when turned.

Par Weber Coefficient Review Eundro-Lume endurolume dial bezel

The bezel rotation is bidirectional.

The entire bezel is the same PVD black as the case. It features a recessed, painted zero in red at the top, and in white at 15 minute increments. Small, machined dots indicate every 5 minutes in between.

Par Weber Coefficient Review Eundro-Lume endurolume bezel

Five minute markings are painted in gloss black.

The bezel is the one part of the watch that could be more functional with a minor modification. As it is only marked in five minute increments, you need to visually estimate the elapsed minutes in between. I'm guessing that Par Weber chose this to give a cleaner look, and less distraction from the time-telling.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The red zero makes it easy to see if the bezel is rotated.

On the flip side, the red zero, and bright white numerals only at the 15 minute marks make it very easy to get a quick visual representation of approximately how much time has passed.


The large PVD black crown is mounted high on the case. It extends across the bottom of the bezel, and partially above the crown guards. It features deep ridges, and does not screw down. All of this is intentional to make the crown very easy to grip and operate.

Par Weber Coefficient Review Eundro-Lume endurolume bezel crown

The large crown is very easy to grip.

The goal is achieved, and it is very easy to adjust the time and date on the Coefficient, even while on the wrist. Again, because this is not a dive watch, I have no problem with Par Weber using a push-pull crown. Having no threads eliminates a possible failure point, and a properly gasketed crown should be enough to guarantee no water gets into the watch during activities like hand washing or swimming in a pool (you know, things that that normal people actually do). A friend of mine recently ruined his watch case by cross-threading the crown.

Large crown guards provide protection, but are mounted low on the crown to make it easy to grip. I assume that the high-mounted crown is because the movement is packaged above the second battery, but the side-benefit is that the crown never digs into your wrist.

Par Weber Coefficient Review Eundro-Lume endurolume crown on wrist wearing

The crown is mounted high in the case, giving plenty of wrist clearance.

The crown has a gap to the case, even when pushed in all the way. It caused me to check that it was secure a few times, but it makes it very easy to pull out to adjust the time.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The crown is pushed in all the way in this photo. That small gap is to make it easier to pull out while on-wrist.

It's apparent how much effort was put into making the crown easy to use and grip. This is especially thoughtful, since an accurate quartz movement means you'll likely be using it less often than on an automatic watch.


As you might expect in a watch designed to be functional and durable, the Coefficient has a flat sapphire crystal with anti-reflective (AR) coating on the underside.

Par Weber Coefficient Review Eundro-Lume endurolume wearing

Flat sapphire makes legibility great at any angle.

Sapphire has the best scratch-resistance, and combined with AR coating, the best clarity with the fewest reflections. I love the look of a domed crystal, but they always create some distortion when viewed at extreme angles. Similarly, I like the decision not to apply AR to the outside of the crystal, as it could be easily scratched.

The result is as you might expect. The watch is supremely readable from any angle.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The crystal is raised slightly above the bezel...

The crystal is also raised ever so slightly above the bezel, and has a tiny chamfer. This catches the light from the lume at night, looking very cool!

Par Weber Coefficient Review Eundro-Lume endurolume dial glowing lume shot night

...creating a cool ring of light around the circumference at night.


The Coefficient arrives mounted on a single stitch vegetable-tanned calfskin strap with quick release (QR) springbars. In the box, you'll also find a single-pass seatbelt-type nylon strap, plus a strap changing tool. Both straps have matching PVD black stainless hardware.

Par Weber Coefficient Review Eundro-Lume endurolume

The included black leather strap completed the full black look.

The leather strap has red Par Weber text on the under side too.

Par Weber Coefficient Review Eundro-Lume endurolume caseback

Red text and QR springbars are great touches.

Both straps are comfortable, and feel to be of high quality. The tool, plus QR springbars are great touches, as I'm sure many customers will be swapping frequently. Drilled 20mm wide lugs mean the Coefficient will look great on a wide variety of aftermarket straps (including those that I sell on my website).

Par Weber Coefficient Review Eundro-Lume endurolume dial

The bonus green strap with black hardware completes the package.


Sandwiched below the Enduro-Lume unit, the Coefficient packs the Swiss-made version of the Ronda 715 quartz movement. It has 5 jewels, and is repairable.

Par Weber Coefficient Review Eundro-Lume endurolume dial glowing night lume shot

Swiss quartz accuracy.

As I mentioned, the movement, and the Eunduro-Lume unit are powered by separate batteries, with the the lume system is designed to require a battery change at the same time as the movement. Thus, when one dies, it is smart to replace both batteries at that time. Par Weber says that any qualified watchmaker or jeweler should have no problem replacing the batteries. Smartly, both units use commonly available battery sizes.

Par Weber Coefficient Review Eundro-Lume endurolume dial

The battery that powers the lume is designed to last as long as the movement's battery.

Jon commented that he expected a faction of the watch collecting community might not get this watch. I'll call them "quartz-averse" because I would never use the word "snob."

Although I love a good automatic watch, I have a strong appreciation for the most effective, and efficient tool being used for the job. If quartz is installed in an un-interesting watch to make a watch cheaper to produce, then I'm not excited about it. In the case of the Coefficient, Par Weber again set aside form, and chose the right function for the job.

Par Weber Coefficient Review Eundro-Lume endurolume movement

The Ronda 715.

The 2.5mm thick Ronda made it much easier for Par Weber to package the Enduro-Lume unit in the watch without making it the thickness of a hockey puck. Plus, since the lume is powered by a battery, having a second one replaced at the same time adds zero inconvenience to the owner. The result is a wearable, and trouble-free tool that is reliable, and ready to go when needed (plus rated at better than 1s/day accuracy).


At a time when a watch coming out in blue is huge news, it's extremely refreshing to see a small company pushing the boundaries and developing new technology. The fact that they can offer patent-pending technology at a price comparable to many other micro-brand ($599) is impressive.

So is Enduro-Lume a gimmick, or a useful feature? Although I'm spending most of my time in the house now, I can think of a number of situations where this watch would outperform any other.

My son sleeps through the night now, but my new challenge is working from home during COVID. Sometimes I have a short window to put him down for his nap in his dark room before my next virtual meeting. Again I am finding myself checking the time in the dark with a child.

Par Weber Coefficient Review Eundro-Lume endurolume dial

So legible during the day...

"Great, but I don't have kids," you say? The Coefficient would also be a perfect travel watch. Whenever I'm on a long overnight flight, I find myself trying to find ways to charge the lume from an airplane seat. Additionally, I never trust hotel clocks, so it would be a great piece to put on the nightstand next to the bed (and 10% of the cost of other Travel Clocks).

Par Weber Coefficient Review Eundro-Lume endurolume dial

...and especially at night!

For whatever night time activities that you do, The goal of supreme legibility was certainly met in the Coefficient. I've owned watches with Tritium, countless grades of Superluminova, Lumibrite, Lum-Tecs, full lume dials, and Auto El. Par Weber now makes the best wristwatch available for quickly reading the time in the dark, full stop.

Par Weber Coefficient Review Eundro-Lume endurolume dial

Par Weber now makes the best wristwatch available for reading the time in the dark, full stop.

I look forward to seeing where Par Weber will take their designs next. It would be great to have the always-available lume in a more stylish envelope to wear out to a dark dinner and a movie date (not that us dads have much time for that anyway).

And in case you wondered, my son loves the glow of the Coefficient, and the bezel rotation is very friendly to toddler hands. I think he is doomed to a life of watch collecting like I am.

Par Weber Coefficient Review Eundro-Lume endurolume dial

Genuine new tech in an affordable package.

For more information, or to purchase a Coefficient, check out You can also check them out on Instagram @par_weber.

If you enjoyed this review and the photos, please give me a follow on Instagram @strap_habit. Thanks for reading!

Your Thoughts?

Do you think that the Coefficient is the ultimate solution for watch legibility? Let us know in the comments!

Par Weber Coefficient Review Eundro-Lume endurolume dial glowing
Par Weber Coefficient Review Eundro-Lume endurolume wrist shot
Par Weber Coefficient Review Eundro-Lume endurolume dial
Par Weber Coefficient Review Eundro-Lume endurolume
Par Weber Coefficient Review Eundro-Lume endurolume
Par Weber Coefficient Review Eundro-Lume
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Hi Kyle, so I’m sorry, that strap was included with the watch. I don’t have any info on where to get one other than contacting Par Weber.


Do you guys make the green strap that was featured in these photos? Or any clue on where to get one?


Great review. I actually got one of the original lot he made and have loved it. Does anyone know what happened to the company? Website is gone and there is no social media activity at all.


Hi Bradley, I have not had any contact with Jon since the original review, so I am not sure what is going on.


Wondering why they are unavailable for purchase. Can you fill me in. For at least a year when going to their website it says sold out. That seems strange , if the demand is there for the product. Thanks

Bradley Dugan

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