SAG mills (Semi-Autogenous Grinding mills) and ball mills are commonly used in the mining industry for grinding ore and other materials. Both types of mills are commonly used in comminution circuits, and their performance can have a significant impact on the efficiency and profitability of a mining operation. SAG mills are typically large, cylindrical rotating drums that are partially filled with steel balls or rocks. The ore is fed into the mill, and as the drum rotates, the grinding media crushes and grinds the ore into finer particles. The primary advantage of SAG mills is their ability to handle large amounts of material at once, which makes them ideal for large-scale mining operations. Ball mills, on the other hand, are smaller, rotating cylindrical vessels that are filled with grinding media (such as steel balls) and the material to be ground. As the mill rotates, the grinding media crushes and grinds the material into a fine powder. Ball mills are commonly used for grinding smaller amounts of material and are typically used in laboratory settings or for smaller-scale mining operations. To predict the performance of SAG and ball mills, a variety of calculations can be used. One common calculation is the Bond Work Index, which measures the energy required to grind a material from a given feed size to a specified product size. This index is used to estimate the energy required to grind ore in SAG and ball mills and is a useful tool for comparing different types of mills and evaluating the efficiency of comminution circuits. Other factors that can affect the performance of SAG and ball mills include the size and type of grinding media, the speed of the mill, the feed rate, and the level of ore in the mill. By taking into account these factors and using appropriate calculations, mining operators can optimize the performance of their mills and improve the efficiency and profitability of their operations. How long will it be before the bond specific energy calculations will be replaced by the morrell specific energy calculations methods.