Quote Originally Posted by BeakerBob View Post
Most of the refractometers sold for this hobby are not linear in their measurement from 1.000 to 1.040. Because of that, they should be calibrated at or near their point of use.

If you want an accurate and consistent (precise) measurement at 1.008, I would calibrate with RO water.

Alternatively, you could purchase a laboratory grade refractometer that is linear from 1.000 to 1.040 or get a calibration fluid that measures 1.010 and use the current refractometer.

You can always dilute the current calibration fluid in half to get a 1.013 fluid.
Bob,

How does this one measure up in your opinion?: http://www.aquacave.com/milwaukee-sa...0atc-616.html#