How do you know where to put the dial thingy for your fridge temperature?

I rent an apartment, and the fridge in it comes from a company that doesn't exist anymore. There's NO instruction manual for it, and I'm not sure if I have it high enough. I have it on 4 out of 7, which is good enough for the winter, but in the summer, I have no idea where to put it. Any suggestions?
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