In a local competition, four contestants are provided with a selection of ostrich eggs as their unusual ingredient, from which they must pick only one to cook with. In order to select the biggest egg for their dishes, the assistant chefs must find the largest ostrich eggs available.

Each of the four assistant chefs chooses an egg and measures its diameter four times, in the interest of improving the accuracy of their measurement. Now they need to report the diameter of their chosen egg to their head chef, but they're not sure what to do with their four separate measurements. Throughout the next sections, your job will be to invent a method that each assistant chef can use to yield a single value, which they can then report as the diameter of their ostrich egg.

What will be a procedure to help each assistant chef calculate a single value to report as the diameter of their ostrich egg? Each assistant can report only a single value as the diameter of the egg. The exact same procedure must be used for each dataset.

What could be a general formula for the index that can calculate a single value for each chef?