There is a simple distinction between these two words that many people have difficulty in remembering.
Continuous denotes an uninterrupted action or state of being that happens over a period of time:
While he talked, he pounded the podium continuously.
Continual refers to action or state of being that happens periodically but often.
Their bickering was continual.
I would put this distinction under the “only for publication” category of usage. It’s common for people to use these words interchangeably, and it’s a rare listener or reader who will cringe at their “misuse” or misunderstand which meaning is intended. For instance, “They were continuously late to meetings” is clear enough and does no harm to the speaker, while “They was continually late to meetings” would jar most business people’s sense of good grammar and would do harm to the speaker.Google+