would someone please tell me about the brix measuring device?

What is it called?

Are there different models eg for range of readings, etc?

Are there any consumables associated with the use of the device?

How do you go about measuring the brix say of
        a potato
        broccoli
        kale
        dried fig
        a piece of meat

Could it make sense to measure the brix of one's saliva/other body fluid?


TIA
Lynton