 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 zinc half cell attached to a standard hydrogen half cell. Electrons flow from the zinc half cell to the hydrogen half cell. The voltage reads 0.76 volts. This indicates that the hydrogen half cell has a greater electron attracting ability than the zinc half cell. Half cells with a lower electron attracting ability than the standard hydrogen electrode are assigned a negative sign. The standard zinc half cell has a voltage of minus 0.76 volts.