What calculates the change in stock prices shown on the indexes? A machine or?

Question

Especially the stocks that change values alot ?

Answer 1

Each stock is given a weight including any dividends.  The weight is based totally on the whim of the person that created the index.  A computer keeps track of the second by second worth of the index.  

Almost all transactions are also done by computer with their formulas trying to get some sort of edge in the stock exchanges.