digital vs naked eye you decide

[Aqua-Digital]

As its digital and does not rely on a refractive index you can use any known value saline solution that is in tolerence with the ppm value the meter is designed to be calibrated to.

This is the difference of refractive vS digital, digital is not bothered about water pollutants that can throw off a refractive index, this is why you can use either NSW or NACL with them and why they are more accepted in laboratories for better accuracy.

You cna get digital refractive such as Hanna, this is basically an auto refractive refractometer, but works on the same principle as a refractometer. This is why you have to state iif you want it for marine or chemical use when purchasing.

Calibrating a digital is simple - place in solution - hold down button - wait a few seconds - calibrated.