While reviewing “no name” refractometers, I read that the Duplex II is the only refractometer designed specifically for spot readings. As I discovered, the “no name” brand units were almost useless at spot readings. I was left wondering how much their smaller size had to do with that.

As an experiment, I purchased a Rayner Dialdex. It’s considerably smaller than the Duplex II and about the same size as a “no name” brand. Both of these instruments are expensive. New, the Duplex sells for around $625. (Editor’s note: You can find used Duplex II and Dialdex refractometers for sale online at lower prices).

How do they compare?

Ease of Use

At first, I found the Rayner Dialdex very awkward to use. However, I soon got comfortable with it. In fact, I remembered I also found the Duplex II awkward at first. So, this one is a tie.

Polarizing Filter

One of the first things I noticed about the Dialdex was the polarizing filter. It made the display much darker and noticeably harder to read. I learned to take it off, except for those occasions when I actually needed it. The filter on the Duplex II never…