What is electrochemical series? How it used to determine the e.m.f. of the cell?

Explanation

Electrochemical series : In order to measure the electrode potential of any electrode, it is connected with standard hydrogen electrode. Then E.M.F. is noted. This E.M.F. gives electrode potential of the given electrode, as the electrode potential of standard hydrogen electrode is zero. this electrode potential can either be positive or negative. the electrode potential of an electrode is given a negative sign if oxidation takes place at this electrode when connected to hydrogen electrode. the standard electrode potential of an electrode is given a positive sign if reduction takes place at this electrode when connected with standard hydrogen electrode to form the cell.
The standard electrode potential of various electrode are given in the decreasing order of their reducing strength, in a series called electromotive force series or electrochemical series.