3-Way Soil Meter (Light/Moisture/pH)

-------------Mercari Auto-Generated----------------------------------
A 3-way soil meter that can measure humidity, light, and pH.
- Type: 3-way soil meter
- Functions: Measures humidity, light, and pH
- Accessories: Instruction manual (printed on packaging only)
- How to use: Insert into soil to measure
- Measurement range: Measures humidity, light, and pH
-------------Description----------------------------------
There is no instruction manual. I will paste a translation of the English text on the packaging in photos 4-6.
-------------My Personal Supplementary Explanation----------------------------------
- No batteries are required. It seems you just insert the pointed tip into the soil.
[Speculation on Operating Principle]
■ Brightness: The analog meter is moved by the photovoltaic effect of a solar cell. I can easily understand this.
■ Humidity: I don't understand the operating principle. I suspect it's an electromotive force due to the difference in ionization tendency of dissimilar metals, similar to pH concentration, but I can't understand how it works with plain water, which is neither sulfuric acid nor saltwater like a Voltaic cell/Daniell cell. It seems to use the left metal of the two. It looks like stainless steel and the tip part is lead? When I tried it by putting tap water in a cup, the meter moved energetically for some reason. Of course, it won't move if the soil is dry.
■ pH concentration: This measures acid/alkali concentration rather than plain water, so I can somewhat understand it from a lemon battery (principle of Voltaic cell). It seems to use the right metal of the two. It looks like aluminum and the tip part is lead? When I tried it by putting tap water in a cup, the meter barely moved. I confirmed that the meter moves energetically when 50mV is applied to the aluminum-lead on the right. I haven't been able to test if it's measuring pH properly because I don't have acidic or alkaline soil on hand. I don't have the energy to squeeze a whole cup of lemon. If there were hydrangeas blooming nearby, I might be able to tell by inserting it there, but they haven't bloomed yet.
[Note] Due to the box size limitations of Yu-Packet Plus, the item will be shipped with the packaging removed. The packaging will be lightly folded and included.