Marine Depot Refractometer

I'm kinda confused here. Anyone used this unit ? It say to calibrate with distilled water to set the line to zero. Also says to do it in a room that's 68 degrees. After getting up one morning with my apartment at 68 degrees I calibrated it. Set it at zero. Does anyone else calibrate in a room at 68 degrees ? There is a difference where the line is with distilled water depending on the temp of the room.

 

Temp does matter.
I have one that needs to be calibrated with 35ppm water. It says calibrate at 77 degrees.
My other is like yours calibrated to zero with RO water but I haven't seen it specified with a temp. If it says do it at 68 then I would do it at 68 unless you can find a chart somewhere to figure out what it should be at a certain temperature.

 

Actually it's my solution that says calibrate at 77 so you could just get some solution and calibrate at 77.