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The fairest comparison is between Seiko’s SSVW213 and Cartier’s Tank Must SolarBeat. Both are rectangular, both run on solar power, and both sit in the same general style family. They differ sharply in brand positioning, and the price comparison is harder than it looks because the two manufacturers publish prices in different currencies and markets. Seiko’s SSVW213 is the lower-cost, radio-controlled option. The Tank Must SolarBeat is a dress-watch-style solar piece from a luxury house, offered in two sizes and two strap or bracelet configurations.
Which models are being compared
“Seiko solar rectangular watch” and “Cartier Tank” each describe a family of products rather than a single watch. A meaningful comparison needs named references on both sides, so the sections below use these two:
Seiko SSVW213
The SSVW213 is a rectangular solar watch with radio-wave control, listed in Seiko’s 2024–2025 Japan-market catalog. It uses Cal. 1B32 and has a stainless-steel case. Because the listing is a Japan catalog entry, it reflects Seiko’s Japanese lineup at that time rather than a current listing in the United States or elsewhere.
Cartier Tank Must SolarBeat
Cartier’s US Tank collection page lists the Tank Must SolarBeat in two sizes, Small and Large, with a choice of calfskin strap or steel bracelet. The SolarBeat is the photovoltaic (solar) version of the Tank Must line. Its name is not the same as the Tank Must quartz models, which are a separate movement and a separate comparison.
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- Includes individual box, instruction manual (English language not guaranteed)
- Solar
- Approximately 10 months when fully charged
- Average monthly difference ±15 seconds
- Calendar (date) function
Other Cartier Tank variants
Cartier sells several Tank lines and also sells Tank Must quartz watches. Those quartz variants are not covered here. If you are shopping for a solar Tank, make sure the listing specifically says SolarBeat; the Tank name alone does not tell you the movement.
Size: what can and cannot be compared
Seiko publishes full dimensions for the SSVW213 in its Japan catalog: 36.3 × 27.7 × 7.7 mm (width × height × thickness). For a rectangular watch, those three numbers matter more than a single diameter figure, because the case shape determines how the watch sits on the wrist and how much it overhangs the strap.
Rank #2
- Tachymeter Feature: Measure Speed
- Secure Case Back: Screw Type
Cartier’s US collection page confirms that the SolarBeat comes in Small and Large sizes, but the captured collection view does not give case dimensions for either size. Any width or thickness figure for the Tank Must SolarBeat should therefore come from Cartier’s individual product page or a spec sheet for the exact reference you are considering. Until those figures are checked, the size comparison is one-sided: Seiko has published numbers and Cartier’s cannot be stated from the sources used here.
Movement: solar, radio control, and quartz
Both watches are solar-powered, but they are not identical in what the movement does.
Rank #3
- GREEN DIAL: this men's watch features a green sunray dial with gold accents, two-tone stainless steel watch case and bracelet, and world time bezel
- LUMIBRITE HANDS & MARKERS: never struggle to tell the time in low light conditions again, thanks to the LumiBrite dial indicator hands and markers
- RADIO SYNC SOLAR CHRONOGRAPH: this Seiko chronograph watch automatically receives radio signals to precisely adjust the time and calendar, ensuring accurate timekeeping
- TIME ZONES & DATE CALENDAR: with three subdials and a handy calendar function, this GMT watch keeps track of the date and world time right on the watch face
- ENERGY-EFFICIENT SOLAR POWER: powered by any light energy, this Seiko solar watch has a power cell that is energy-efficient with a 6-month reserve once fully charged
- Seiko SSVW213: Cal. 1B32, listed under radio-wave-control solar. A radio-controlled watch receives time signals and corrects itself. Reception depends on location and conditions, so these watches are usually designed to work in areas where the signal can be received.
- Cartier Tank Must SolarBeat: described as photovoltaic. Cartier’s page identifies it as a solar model; the sources used here do not establish whether it has any radio-timekeeping function.
- Cartier Tank Must quartz: a different movement family that Cartier sells alongside the SolarBeat. Not part of this comparison.
Solar charging from light is the shared feature. Radio control is a Seiko-specific feature in this pairing, and it is one of the main reasons the SSVW213 is listed in the radio-wave-control category.
Price: what the listings show and why they do not compare directly
Seiko’s SSVW213 is listed at ¥70,400 including tax in its 2024–2025 Japan catalog. Cartier’s US collection page displays the SolarBeat at the following prices:
Rank #4
- Powered by light energy, with no battery change required, this timepiece automatically receives radio signals to precisely adjust the time and calendar and has a 6-month power reserve once fully charged
- Case Diameter: 44.5mm
- The intricately patterned black dial with gold accents features a chronograph, radio signal reception display, power reserve indicator, date calendar, and LumiBrite hands and markers
- The angular two-tone stainless steel case is paired with an integrated bracelet and includes a sapphire crystal and cabochon crown
- Water-resistant to 10 bar, 100 meters (330 feet)
| Cartier Tank Must SolarBeat configuration | Displayed US price |
|---|---|
| Small, calfskin strap | $3,600 |
| Large, calfskin strap | $3,800 |
| Small, steel bracelet | $4,000 |
| Large, steel bracelet | $4,250 |
These two prices are not directly comparable. The Seiko figure is yen and tax-inclusive, from a Japan catalog dated 2024–2025. The Cartier figures are dollars from the US collection page, and the date of that display is not stated in the source. Converting the yen price into dollars would require an exchange rate from a named source on a specific date, and no such rate is part of this comparison. Prices on both sites change, so use the figures as reference points and confirm the current price for the exact reference before buying.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Design heritage
The Cartier Tank’s design story is documented on its own Tank collection page, which states: “The Tank watch was created by Louis Cartier, who designed it after the tanks of WWI battlefields.” The same page describes the design with “flat vertical brancards and a sapphire cabochon.” These are Cartier’s own descriptions of the watch; they are not independent historical verification. Seiko’s rectangular solar models come from a different design tradition, and the SSVW213 entry does not make a comparable heritage claim.
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- All-Black Slip-Thru Style: A black fabric slip-thru strap matches the black resin case and black dial for a clean, all-black look that suits daily outdoor wear
- Solar Powered: Charged by any light source with a four-month power reserve, this outdoor solar watch runs on natural energy and stays ready for the next adventure
- Black Resin Case: A black resin case and black dial give this analog solar watch a clean, rugged look, and the fabric slip-thru strap is made for easy on and off
- Adventure-Ready Style: Inspired by the northern edge of the U.S. Rockies, this solar field watch is a companion well-built for the outdoors
- Built to Last: A Timex watch is designed for durability and everyday reliability; every piece reflects our commitment to quality without compromise
How to compare two options yourself
When you compare any two rectangular solar watches, check the same fields on both:
- Case width, height and thickness. Use all three; diameter alone does not describe a rectangular case.
- Movement family. Solar photovoltaic, radio-controlled, and quartz are different things. Confirm which one the exact reference uses.
- Dial and strap or bracelet configuration. The Cartier configuration changes the price materially; the Seiko catalog entry does not state its strap or bracelet options.
- Price in one currency, with the date and market. Convert only with a dated, named exchange-rate source.
- After-sales support. Confirm warranty terms and service access in the market where you will buy.
Trade-offs to weigh
- Radio control versus a standard solar movement. The SSVW213 adds time-signal correction. That is useful if you want the watch to set itself, but it depends on reception where you live.
- Brand and price tier. The Cartier carries a luxury-house price and a documented design story. The Seiko is positioned at a much lower price point.
- Size data. The SSVW213’s published dimensions allow a clear fit check. The Tank Must SolarBeat’s dimensions should be confirmed on the exact product page before you compare fit.
The Bottom Line
If you want a rectangular solar watch with a published size, radio control and a lower price, the Seiko SSVW213 is the stronger fit on the evidence available. If brand, the Tank design heritage and a steel bracelet or calfskin strap at a luxury price matter more to you, the Cartier Tank Must SolarBeat is the option to consider. Neither price can be turned into a like-for-like figure without a dated exchange rate, and both should be checked directly with the seller or manufacturer before purchase.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
