Purchase date 21/1/2021.
First test on 23/1/2021.
Evaluation day 25/1/2021.
For 3 consecutive days, I measured the humidity in each room with this specific hygrometer and the Pure Dry 8519 dehumidifier.
The measurements are identical, both before and after using the dehumidifier.
Additionally, it detects the difference in humidity and temperature, in case we open the windows or the door from a room with higher humidity.
The external sensor is also extremely accurate, as the values it presents do not differ from the internal sensor when it is in a room with closed doors and windows.
In the case of using a heating device, it shows a gradual decrease in humidity with a simultaneous increase in temperature.
The measurements include one decimal digit.
The screen is indeed large and clear. It does not have a night light feature.
It has a magnet to stick to the refrigerator.
It includes a battery in the packaging.
With the insertion of the battery into the product, it starts functioning and sets itself up after a few minutes.
Conclusion:
An extremely accurate hygrometer and thermometer, which deserves more than 5 stars.
I am very likely to buy 2-3 more as gifts for relatives.
Update one year later:
I have purchased over 10 and have distributed them to relatives and friends, and we exchange our measurements.
Reliable and very sensitive to changes. It crashes above 50 degrees Celsius, so do not expose it to direct sunlight during summer midday. Also, do not put it inside a freezer at -20 degrees.
Update 2: The difference between the dehumidifier puredry pdd-8519 is exactly 2%. Negligible, in other words.
Update 3: New device as of December 2002, it starts measuring the humidity accurately in seconds once opened from the box and batteries are inserted. It does not even need calibration. Impressive.
It has truly changed my life. If I go to a new place, whether urban or rural, I take it with me and measure the humidity of that specific area. Extremely useful, especially for someone with respiratory problems to know the humidity level in their home.
Update 8/1/2024:
All devices are still functioning flawlessly with the same initial battery and the same success. Congratulations!
Update July 2024:
Seeing the negative comments from other users and having 3 identical devices, I wanted to test if they would indeed measure the same side by side...
From February until today, the devices, when placed side by side, give the same measurements.
However, I bought them from different stores each time (due to lower prices).
I don't know... maybe I am lucky and all the models have turned out well for me. What can I say?
Therefore, as long as it remains a consistent and accurate thermometer-hygrometer, my positive evaluation will remain.
I hope I helped...

This specific thermometer - hygrometer OEM DC103 was purchased for 5.6€, so it is directly the first in terms of Value for Money. It replaced a branded AVIDSEN 107240, which proved unworthy of my expectations (and which is also sold as LIFE WES-102, Velamp Therm04 Square +, Konig KN-DTH10).

POSITIVE COMMENTS:
1. It is cheap and displays temperatures at two points (the second point is measured via a wire at a maximum distance of 0.8m from the device), along with humidity in its position. It also keeps max and min measurement memories with a very easy menu. Therefore, it excels in terms of Value for Money.
2. It has large and easy-to-read indicators, ideal for a household refrigerator. Also, with the higher and lower temperature memory it keeps, you can check (and discard or not) food from the refrigerator after a power outage from the power company, as long as a high temperature is recorded during the outage.
3. It has a magnet for hanging, but you need to stick a metal disc to the plastic interior of the refrigerator. The best position in a double-door refrigerator is found to be on the side wall on the second top shelf, and the cable sensor in the vegetable drawers at the bottom.
4. It provides accurate measurements (for its price), which are not far from reality (specifically, it shows about 1 degree C less than two classic alcohol thermometers I placed in the same position).

NEGATIVE COMMENTS:
1. Strangely, the external sensor (the one at the end of the cable) gives faster and more accurate measurements than the internal sensor.
2. It has a small coin-type battery at 1.5V, so given that the display never turns off, it will soon need replacement. It would be better if it had AAA batteries.

CONCLUSION:
Do not pay twice as much for the Medisana HG 100, it is exactly the same, it just has unnecessary Greek instructions. This OEM DC103 is honest for its price and ideal for a household refrigerator.

I bought it exclusively because it has a magnet on the back. This particular model is exclusively for the refrigerator, as the main and larger display it has is practically useless. Who would take the short cable out of the house anyway? If you want it for another room or space in the house, other similar thermometers are recommended.

Personally, I have bought three different thermometers and they show a deviation of exactly ±2 degrees between them when they are placed side by side. I consider the round battery it takes as a disadvantage compared to the other two I have (Konig KN-WS 102 & OEM HUM-HTC-2) which take 1.5V AAA xl batteries.

Of course, like all thermometers in this category, it does not have an internal light, which means that the readings are not visible in a dark room and of course at night.

Anyone interested in a thermometer of this category should know that the readings are approximate, but not far from reality. In other words, to get an idea of the room's condition, it is value for money. If someone wants to know the temperature and humidity in a room with absolute accuracy, they will have to go up a category and spend much more money.