The mean absolute deviation is the average of the positive distances of each point from the mean. The larger the MAD, the greater variability there is in the data (the data is more spread out). The MAD helps determine whether the set's mean is a useful indicator of the values within the set.
95 - 98+. Although Potassium only has two stable isotopes (K-39 and K-41), the long-lived radioisotope K-40 is often also regarded as a stable isotope. Potassium Isotopes, mainly K-40 and K-41, are used to study the impact of potassium on the growth of plants and of the human cardiovascular system.
1 Today, potassium metal is still obtained from electrolysis of potassium hydroxide. Davyâs methods have not been changed very much over the last 200 years.  As potassium reacts rapidly with air, it is very dangerous to transport. It must be stored in something (often kerosene) which stops it reacting with air.