Glass or Plastic Hydrometers?

How can that refractometer not use batteries? Does anybody have this one? How is it? If you guys like it I will probably get one. It worth it when you are spending $65 on polyps etc.
 
How can that refractometer not use batteries?

It's not electronic. Just like the name implies it refracts light. You put a drop of water on it and hold it up to the light. When you look in you'll see a blue area which you compare to the scale on the side.
 
Ya I just read that on the site lol. I guess I didnt put two and two together thanks. I just ordered it. If its a Drs Best on the site it isnt bad.
 
You can get one from my LFS that takes batteries as it has a built in LED so you dont need to find natural light all the time
 
AquariaCentral.com