Cyanometer vs Rhyy
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Cyanometer
Measure the intensity of blue in the sky to understand atmospheric conditions. Save scans with location and time data for comparison across different places. Offers modern, historical, and custom color scales.
- Measure sky blueness intensity
- Modern, Saussure, and custom scales
- Save scans with date, time, and location
- Compare sky conditions across locations
- Privacy-focused, no external data processing
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The original cyanometer was invented by the Genevan physicist and Alpine explorer Horace-Bénédict de Saussure (* 17 February 1740 in Conches; † 22 January 1799) in 1789. It is an instrument for measuring 'blueness', specifically the colour intensity of blue sky. With the measurement it is possible to draw conclusions from the constitution of the atmosphere: the bluer the sky the less the water vapor. Saussures cyanometer consisted out of 53 parts of a circular ring ranging from white over different grades of blue to black (Saussure used Prussian blue). Saussure used his cyanometer for measurements in Geneva, Chamonix und on the Mont Blanc. Alexander von Humboldt used a cyanometer on his expedition to America (1799 - 1804). You can use our Cyanometer in three modes: The modern scale uses distinct grades of blue starting with clear white up to black. The Saussure scale shall give an idea about the colors from Saussures original cyanometer. With the user defined scale own scans of blue skies can be added to an own colored circular ring - an own cyanometer. Each scan is saved inside the app containing information about date, time and locality. So it is possible to compare scans of blue skies from different locations. Privacy notice: No data will be saved or processed outside the app.
Rhyy
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Basel or Rheinfelden: wondering whether the Rhine looks good today? Rhyy gives you the quick pre-swim check on iPhone, Apple Watch and right in your widgets. At a glance, you get water temperature, weather, air temperature, river level, flow and UV index. Rhyy puts the numbers in context, shows how they are developing and suggests a swim window for today and tomorrow. No need to check five different sources before heading to the river. Water quality is more than a row of numbers. Comparison ranges and clear guidance help you understand what oxygen, pH and conductivity mean for your swim – and what those readings cannot guarantee. With Swim Crew, you can anonymously show that you are heading into the Rhine today. Read current community updates, like a post and jump straight to the open form on rhyy.ch when you want to write one. Your swim log stays on your device by default. You can now opt into encrypted sync across multiple devices and rhyy.ch, with no account needed. Add duration, distance, how it felt and a note, then keep your latest swims close at hand. Ideas or something missing? Feedback through the in-app form is very welcome. On Apple Watch, the essentials stay on your wrist. Widgets and complications show water, air, UV, status and the swim window without making you open the full app. Rhyy shows how things look right now. The river still gets the final say: always check conditions on site and only get in when it feels right for you. Rhyy is guidance, not clearance and not a safety or rescue recommendation.
Screenshots
Verdict
The clearest difference is price: Rhyy at Free against Cyanometer's $0.99. Rhyy also leads on update cadence (every 11 days vs every 39 months). Cyanometer's advantage is chart position (#184 vs unranked). On ads, in-app purchases, device support and iOS requirement there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Rhyy is free to download; Cyanometer costs $0.99 up front. Neither carries in-app purchases, so what you see is what you pay.
Cyanometer ships an update every 39 months, Rhyy every 11 days. The most recent releases landed on October 9, 2026 and October 15, 2026 respectively.
| Parameter | Cyanometer | Rhyy |
|---|---|---|
| Price | $0.99 | Free — better |
| Rating | 2.8 (4 ratings) — better | — |
| Positive reviews | 25.0% of reviews | — |
| Number of ratings | 4 — better | — |
| Update frequency | Every 39 months | Every 11 days — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | — |
| Best chart rank | #184 — better | — |
| Devices | iPhone, iPod | iPhone, Apple Watch |
| Requires iOS | 16 — better | 17.0 |
| Further details — not scored | ||
| Size | 14 MB | 10 MB |
| Age rating | 4+ | 12+ |
| Developer | Jan-Hendrik von Kuick | Patrick Habluetzel |
In-app purchases
Cyanometer
No in-app purchases
Rhyy
No in-app purchases









