Refractometer help

[CobraSnake7]

Can someone tell me how to use a refractometer. The instructions say to set it to null. What does that mean, and how do you do it? I understand about the setscrew on top, but what do you do then, how do you read it? When I put a few drops of water on the prism, close the plate, and then adjust it, I see a shadow area that covers most of the numbers inside, but what then? As you adjust, the shadow moves up or down as you move the setscrew, but what then????

 

[joy13]

Did you get calibration fluid with it? If not use pure ro water it isn't as good as the calibration fluid but it will work in a pinch. Turn the set screw until it reads 0 with the calibration fluid or the ro water. I am not for sure if you are referring to the blue part as the shadow or not. Did you get calibration fluid with it? If not use pure ro water it isn't as good as the calibration fluid but it will work in a pinch. Turn the set screw until it reads 0 with the calibration fluid or the ro water. I am not for sure if you are referring to the blue part as the shadow or not.

 

[CobraSnake7]

No, I don't have any calibration fluid. I borrowed this thing, and I still need to know what the null is, and what do I set this thing to. I used my water, set it to "0", wiped it dry, put a few drops from my sw tank,
and it read 1.025 I used my hydrometer plastic tool, and it read 1.024, so I guess it's close enough. Maybe I used it correctly, but I don't know for sure. Thanks for the info. Larry

 

[joy13]

Unless there has been a big temperature change it should have stayed calibrated my friend left his out in the car for a couple of days and had to recalibrate but it has been accurate every since. The refractometer is much more accurate than the hydrometer one bubble on the arm can throw it way way off.