This Rayner Dialdex is from my personal collection.
In spite of the fact that they haven’t made these in quite some time they’re still fairly common, running in the $700 to $800 range online. But this is the only one I’ve seen with the base, which acts as a stand and a light source.
The light runs on either 9v DC or 120v AC and attaches to the back of the refractometer, making it more convenient than having to break out your polariscope to provide a light. Although you can use an external light by unscrewing one thumb screw and removing the connection on the back of the device.
I’m told that the Rayner is more accurate than the GIA Duplex II but I write such talk off as personal preference not proven fact. It’s sort of like saying Ford is better than Chevy.
For instance I have a cheap Chinese refractometer with a built in light that has proven to be as accurate to two places as my Duplex II. –It is not as comfortable or as easy to read but with care the results are consistent.
If you’re curious this comparison of the Duplex II and the Rayner Dialdex is fairly neutral.
Whatever instrument you choose practice until you get good at it before passing judgement.
–Bad tools will make you crazy, but good tools used badly will make the rest of us crazy.