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Discover how a mechanical hygrometer works: how to measure humidity levels, read the dial, and understand this measuring instrument – a battery-free hygrometer.
How does a hygrometer work?
A hygrometer is an instrument used to measure the moisture present in the air, also known as relative humidity. Once mainly reserved for weather stations and technical equipment, it is now widely used throughout the home to monitor indoor comfort, reduce condensation, and help prevent mould growth.
Reading a hygrometer is relatively simple. The pointer directly indicates the percentage of relative humidity present in the air. Thanks to this instant reading, it becomes easier to understand the balance of humidity in your home.
• Below 40%: dry air
• Between 40% and 60%: comfortable humidity
• Above 60%: humid air
The ideal humidity level in a bedroom is generally between 40% and 60%. This range helps improve respiratory comfort and reduces the sensation of excessively dry air.
A good humidity level helps create a more comfortable living environment every day, especially in a bedroom or nursery.
For a wine cellar, a humidity level of around 70% is generally recommended to help preserve wine bottles in optimal conditions.
According to ADEME and several health organisations, excessively humid indoor air can encourage mould growth and reduce indoor air quality.
The operation of a hygrometer is based on the reaction of a sensitive element to the moisture present in the air. As the humidity level rises or falls, this element expands or contracts. This mechanical movement then causes a needle to move across the dial.
Our mechanical hygrometer operates without batteries thanks to a metal mechanism that naturally responds to changes in air humidity, moving the needle across the dial.
The principle of the mechanical hygrometer has been used for many years. It remains popular today for its simplicity, reliability and timeless design. Unlike an electronic model, it does not rely on a screen, batteries or a power supply.
Relative humidity refers to the amount of water vapour present in the air, compared with the maximum amount that the air could hold at a given temperature. It is expressed as a percentage.
Example: air at 50% relative humidity contains approximately half of the water vapour it could hold before condensation occurs.
The humidity level in a home naturally changes throughout the day. It is influenced by indoor temperature, ventilation, the seasons, the property's insulation, and the presence of water or water vapour in the air.
Poor air circulation can encourage indoor condensation and increase the risk of mould growth. Reading a hygrometer therefore helps you monitor the balance of humidity in your home more effectively.
When humid air comes into contact with a cold surface, it may reach what is known as the dew point. Small droplets then appear as condensation on windows or walls. A hygrometer helps monitor humidity levels and anticipate these effects.
🔧 Every hygrometer is checked and calibrated in our workshop before dispatch.
A quality control card included in the package details the calibration performed and the first name of the person who carried out the adjustment.
Before dispatch, every Ocean Clock hygrometer is calibrated in our workshop to ensure consistent and reliable relative humidity readings. This calibration is carried out under controlled conditions directly in Hossegor.
Like all humidity measuring instruments, slight variations may nevertheless occur depending on the environment in which the hygrometer is installed, including ventilation, heating, proximity to a window, temperature and air circulation.
If you already have a weather station or another reference hygrometer in your home, it is possible to make a small adjustment to your Ocean Clock hygrometer in order to obtain a similar reading.
To compare two hygrometers correctly, it is important to place them side by side in the same room for several hours so that they stabilise under identical conditions.
A small adjustment screw located on the back of the hygrometer can then be used to fine-tune the needle position if necessary.
However, we recommend avoiding frequent adjustments. The most important thing is to observe overall changes in humidity levels within your home rather than focusing on an exact percentage value.
To ensure stable and consistent relative humidity readings, we recommend installing your hygrometer in a naturally ventilated room, away from extreme variations in temperature or humidity.
Temperature and humidity levels may require several hours to stabilise after installation.
To maintain reliable humidity readings, avoid exposing your hygrometer directly to:
We also recommend avoiding installation in a bathroom or too close to a window, as this may affect the accuracy of the reading.
The droplet-shaped spacers located on the back of the hygrometer allow a small amount of air to circulate between the wall and the instrument.
This natural airflow promotes more stable and accurate humidity readings.
Relative humidity is expressed as a percentage (%). The hygrometer has a measurement accuracy of ±4%.
The operation of a hygrometer is based on the reaction of a humidity-sensitive element to the moisture present in the air. As humidity levels rise or fall, this element expands or contracts, causing the needle to move across the dial.
The Ocean Clock hygrometer operates without batteries. It uses humidity-sensitive materials to move a needle mechanically. Like other Ocean Clock measuring instruments, it is a low-tech product, designed to last and function with simplicity.
No batteries, no screen, no charging required: the bimetal hygrometer displays humidity levels through a simple and durable mechanical movement.
Each wooden hygrometer is hand-assembled in our workshop in Hossegor, in south-west France. Inspired by the world of the ocean and traditional measuring instruments, our models combine minimalist design, mechanical operation and French craftsmanship.
There are several types of hygrometers. A hair hygrometer uses a natural hair or a humidity-sensitive fibre. As the air becomes more humid, the fibre relaxes slightly. When the air becomes drier, it contracts. This movement mechanically drives the dial needle.
A mechanical hygrometer, on the other hand, measures air humidity without any electrical power source. It provides an immediate and easy-to-read indication while maintaining an attractive decorative appearance.
Depending on the model, the sensitive element may be an electronic humidity sensor, natural hair, a synthetic fibre or a bimetal mechanism.
| Type of hygrometer | Power source | Accuracy | Maintenance | Appearance |
|---|---|---|---|---|
| Mechanical hygrometer | Battery-free | Good accuracy when calibrated | Low | Highly decorative |
| Electronic hygrometer | Battery-powered | Very accurate | Battery replacement | More technical appearance |
| Digital hygrometer | Battery or USB powered | Very accurate | Charging or battery replacement | Modern screen-based design |
A hygrometer helps you better understand the air inside your home: whether it is too dry, comfortably balanced or excessively humid.
The ideal humidity level depends on the room and its use. A hygrometer makes it easy to check whether the air in your home remains within a comfortable range.
| Room | Recommended humidity level |
|---|---|
| Living room | 40–60% |
| Bedroom | 40–60% |
| Nursery | 40–60% |
| Wine cellar | Around 70% |
Air that is too dry can cause discomfort or irritation, while excessively humid air encourages condensation, unpleasant odours and mould growth.
Reimagined hygrometers
informations
An indoor hygrometer allows you to easily monitor the level of humidity in the air within your home. Although often unnoticed in everyday life, maintaining the right humidity balance plays a vital role in indoor comfort, air quality, and overall wellbeing in a room.
➡︎ Air that is too dry can cause discomfort, while excessively humid air encourages condensation, unpleasant odours, and mould growth. With a needle hygrometer, you can keep a simple and immediate eye on the relative humidity level in your home.
Whether in a bedroom, living room, nursery, or even a wine cellar, monitoring humidity makes it easier to adjust ventilation and maintain a healthier, more pleasant environment every day.
A mechanical hygrometer operates without batteries thanks to a sensitive element (either natural hair or a synthetic fibre) that expands or contracts according to the humidity level.
Ocean Clock offers a more decorative and sustainable approach to this measuring instrument with its battery-free mechanical hygrometers, hand-assembled in France in our workshop in Hossegor. Designed as genuine decorative objects, they combine elegant design, natural wood, and battery-free mechanical operation.
A battery-free hygrometer measures air humidity using a mechanism that responds to changes in relative humidity. As the air becomes more humid or drier, the mechanism naturally reacts, causing the needle to move across the dial. It operates without batteries, electrical connections, or a display screen.
A hygrometer measures the humidity of the air, expressed as a percentage of relative humidity. A moisture meter, on the other hand, measures the moisture content within a material such as wood, plaster, or concrete. Both instruments measure moisture, but they are designed for different purposes.
In a bedroom, a humidity level between 40% and 60% is generally considered comfortable. This range contributes to respiratory comfort and helps prevent the air from becoming either too dry or too humid.
Measurements can be influenced by the environment in which the device is installed. Positioning it near a window, radiator, heat source, or source of moisture may affect the reading. After installation, it is also normal for the hygrometer to require several hours to stabilise. The measurement accuracy of our hygrometer is ±4%.
Every Ocean Clock hygrometer is checked and calibrated in our workshop before dispatch. If you wish to adjust it to match a reference weather station, place both devices side by side in the same room for several hours. A small adjustment screw located on the back of the hygrometer can then be used to fine-tune the setting if necessary.
Fun facts about humidity
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