 In order to assign a voltage to a standard half cell, we attach the half cell to a standard hydrogen electrode. Here we have a standard copper half cell attached to a standard hydrogen half cell. Electrons flow from the hydrogen half cell to the copper half cell, and the voltage reads 0.34 volts. This indicates that the copper half cell has a greater electron attracting ability than the hydrogen half cell. Half cells with a greater electron attracting ability than the standard hydrogen electrode are assigned a positive sign. The standard copper half cell has a voltage of positive 0.34 volts.