How to adjust refrigerator temperature/power? On my refrigerator, there's a wheel (1-5) to adjust temperature/power, but there's no indication about it - is it power (1 is low power and 5 is max power with max cold) or are those numbers the temperature?

It not the first time I come across refrigerators with that kind of setting, and I eventually always try a low and high number and try to compare between them about how it feels.

I have a simple refrigerator of Electra, and it has no indication I can see about a model.

Is there a standard for this? How can I know what the wheel numbers mean?
There is no standard, and you cannot know what the numbers mean, at least without the user manual. If it is important for you to keep a certain temperature, get a fridge thermometer and use that. Be certain to measure in multiple places, or in the place you are most interested in because the temperature varies throughout the refrigerator body. 

A second way would be to try to jump through hoops with customer support (maybe send them a photo of the refrigerator? or turn it around and see if you have a model label and/or serial number somewhere around the compressor) and have them locate a user manual for you, or maybe even the temperature itself. But this will only give you the temperature the designers intended, which is not exactly the same as the actual temperature in the fridge.