Just peel off the sticker’s backing and permanently affix to your carboy or fermenting vessel. Sticks to plastic, stainless steel, or glass to accurately read temperature of vessel. More accurate than thermometer next to fermenter because during primary fermentation the yeast activity raises the temperature a few degrees. Liquid crystals change color as temperature rises and falls. Lasts for years. The larger size features a range of 44-86 Farenheit along with a helpful guide to where your lagers, ales, Belgian-styles,and white & red wines should ferment.