Excellent accuracy. This thermometer shows the highest temperature achieved and stays there. Then one has to "shake" or "whip" the mercury down again, as with a fever thermometer. With this thermometer one can watch to see that the temperature in the fermentation does not reach killing temperature or pass "quality" temperature when fermenting mash or a base for alcoholic beverages. It's a good instrument for old, traditional distilleries without the latest technology to make sure that the mash does not reach killing temperature. Length 20 cm.