With classic computers, all we have to worry about error correcting is the bit flip, but with quantum computers there is another type of flip that is possible: the phase flip. This flip is the equivalent of the Z gate acting upon the state. So the states |"0"> and |"1"> would be unchanged by a phase flip, while a state |"+"> or a state |"-"> would flip to the opposite state. The good news is that to correct this error, we can use a very similar circuit to the bit flip code. Recall that the H gate changes the |"0"> state into the |"+"> state. Any phase error on a single qubit would change the |"+"> state into the |"-"> state. Finally, if we apply another H gate, we would get the |"1"> state after this error. So, if we surround the portion in which a phase error is potentially introduced by H gates, we can transform on either end the phase error into a bit flip error and use the same bit flip code to detect the error. Then, to correct for the error, we apply the Z gate. Now that we can address both single bit flip errors and single phase flip errors, we are ready to address any single qubit error.