EMF of a cell in terms of reduction potential of its left and right electrodes is

According to IUPAC , the galvanic cell is represented 

LHS = Anode 

RHS = Cathode 

${{\mathrm{E}}^{\mathrm{o}}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{cathode}}-{\mathrm{E}}_{\mathrm{anode}}$

Therefore 

${{\mathrm{E}}^{\mathrm{o}}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{right}}-{\mathrm{E}}_{\mathrm{left}}$