There are so many gadgets available for the home brewer and I freely admit that I have bought quite a few of them. Sometimes I even end up with the right gadget at the right time and that is how I felt about the vinometer.
Using the vinometer is easy. First, position the cupped end upright. Next, add about a milliliter of wine or cider to the cup and wait until drops begin to work their way out of the bottom of the tube. Finally, invert and watch the column of fluid drop until it stops then read the alcohol percentage from the scale.
Easy right? Well, there is one one catch. The vinometer really only works accurately for dry wines. I also have had luck using it with dry ciders where the SG is at or under 1.000. It works by capillary action where the specific gravity and surface tension cause the column of the liquid being measured to drop until an equilibrium is achieved. Alcohol lowers surface tension, so the higher the alcohol content, the further the column drops down the tube. Any residual sugars will cause your readings to be low as the sugar will increase the surface area. This makes it not so handy for beer, but certainly can be helpful for country wine, cider and perry where getting an accurate initial SG can be challenging due to the fruit solids in the must.