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Citizen BY1018-55X Super Titanium™ 'Tsuki-Yomi' Moon Phase Watch - W38380
Ref. BY1018-55X
Sits in Citizen’s upper tier here — more premium than three quarters of the Citizen watches we list, which start at £139.
Price range £139 to £1,145 across 113 Citizen watches in stock.Tsuki-Yomi translates as "reading the moon", and the name is precise. This collection was created to mark thirty years of Citizen's radio-controlled watchmaking, and the H874 calibre at its heart represents what that anniversary warranted: the world's first light-powered radio-controlled moon phase movement. The mechanism behind the display is Citizen's proprietary Luna Program, a mathematical formula that draws on atomic clock signals from multi-band transmitters to calculate the moon's phase each day and adjust the analogue display accordingly — automatically, with no manual correction required. The red dial is textured to suggest the lunar surface rather than simply represent it, and the result reads very differently across lighting conditions: closer to a relief map under direct light, considerably more atmospheric in shade. Despite the 43mm case, the 48.5mm lug-to-lug measurement means it sits flush against most wrists without overhang, and the Super Titanium construction with Duratect coating keeps it considerably lighter than a steel watch of equivalent size — that combination of depth rating, complication density, and barely-there wrist presence is genuinely unusual. The integrated bracelet tapers from 22mm at the lug to 20mm at the dual push-button deployment clasp, which gives it a clean, uninterrupted line from case to wrist. With a six-month power reserve and a native accuracy of ±15 seconds per month between signal syncs, this is a watch that asks almost nothing of its owner in return for everything it is tracking.
- Reference
- BY1018-55X
- Brand
- Citizen
- Collection
- Tsuki-Yomi
- Case size
- 43mm
- Case thickness
- 11.4mm
- Lug width
- 22mm
- Case material
- Titanium
- Case shape
- Round
- Dial
- Red
- Crystal
- Sapphire
- Movement
- Solar
- Calibre
- H874
- Functions
- Day-date, Moonphase
- Water resistance
- 100m
- Bracelet / strap
- Titanium bracelet
- Strap colour
- Silver
- Clasp
- Deployant clasp
- Lume
- Luminous
- Retailer
- Mappin & Webb
Additional specifications
- Lug-to-lug
- 48.5mm
Learn more about Citizen
The Shokosha Watch Research Institute began in Tokyo in 1918, and the Citizen name was given to its first pocket watch in 1924 by the then mayor of Tokyo, Shinpei Goto, who wanted a watch that would be available to ordinary citizens rather than only the wealthy. The company formally took the name in 1930.
That founding intention has held. Citizen is the largest watch manufacturer in the world by volume and is fully vertically integrated, making its own movements, cases, and electronic components.
Its most significant technology is Eco-Drive, introduced in 1976 and refined over decades. A photovoltaic cell beneath the dial converts any light — including indoor light — into stored energy, so the watch never needs a battery change. Citizen has sold well over a hundred million Eco-Drive watches, and the environmental argument is substantial: hundreds of millions of cells not discarded.
The company also produced the first analogue quartz watch with a titanium case in 1970, the first professional dive watch with an electronic depth sensor, and the Caliber 0100, an Eco-Drive movement accurate to within one second a year — the most accurate independent watch movement ever put into production.
Citizen owns Bulova, Frederique Constant, Alpina, and the movement manufacturer Miyota, whose calibres power a large share of the affordable mechanical watch market worldwide.
- 1918
- The Shokosha Watch Research Institute is founded.
- 1924
- The Citizen name is given to its first pocket watch.
- 1976
- Eco-Drive light-powered technology is introduced.
- 2018
- The Caliber 0100 achieves accuracy of one second a year.
Also in 2 collections
This watch appears in Solar & Kinetic Watches (263) and Titanium Watches (186).
Manufacturer’s guarantee
Best of 3 retailers
What the specifications mean
Strengths
- 100m water resistance covers swimming and watersports
- 48.5mm lug-to-lug keeps the 43mm case wearable
- Sapphire crystal, which resists scratching
- Luminous hands and markers for low light
- One of Citizen's more premium watches
Worth knowing
- 43mm sits at the larger end
Citizen BY1018-55X Super Titanium™ 'Tsuki-Yomi' alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification |  BY1018-55X | SFJ009P1 | 010-02582-21 |
|---|---|---|---|
| Price | £699 | £665 | £630 |
| Case size | 43mm | 42mm | 47mm |
| Water resistance | 100m | 100m | 100m |
| Movement | Solar | Solar | Solar |
| Strap | Titanium bracelet | Stainless steel bracelet | Silicone strap |
| This watch | Closely matched |
|
Your new watch
Frequently asked questions, and things you should know about this watch
Can I swim with it?
Yes. At 100m it is rated for swimming and snorkelling, though not for diving.
Water resistance explainedWill the glass scratch?
Unlikely. Sapphire is second only to diamond in hardness and shrugs off everyday marking.
Sapphire, mineral and acrylic comparedDoes it need a battery?
No. It charges from light, and the cell behind that is designed to last a decade or more.
Quartz, automatic and solar comparedWhat size strap does it take?
22mm. Any strap of that width will fit, and on most modern watches quick-release bars make the swap a two-minute job with no tools.
Will it fit my wrist?
Lug-to-lug is 48.5mm, which suits wrists from roughly 16.5cm (6½ inches) upward.
Lug-to-lug decides fit more than case diameter does.
How to size a watch to your wristIs it a men's or women's watch?
Listed as men's.
Cheapest place to buy
All 3 UK retailers we track list it at £699.
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