I have one, I like it best of any I have ever used, which is the reason I have it. In addition to giving the freeze point/concentration for Ethylene Glycol and Propylene Glycol, it also will give you the specific gravity(state of charge) of battery electrolyte. It is(was) made by Leica and is a model DC-84. The division of Leica that made these is now Reichert Analytical instrunments. The current comparable model(Looks identical, but different color) is a DC70, and costs around $80 according to their website. You can look at the tech info and manuals at the below listed website. The last page of the manual shows a sample of the display. It is very precise and shades half of the display when a sample is placed on the glass window. The line between light and dark is the measurement of that sample Reichert Products - Engine Coolant/Antifreeze and Battery Tester - Overview
I'll second Ron's suggestion of a Leica refractometer. I have had a couple of them for years and it's the only thing I will use to check antifreeze concentration.
Thanks for the info guys. I was somewhat overwhelmed after googling the refractometers, had no idea there were so many. The DC70 looks like the one I want. Thanks again,