The Past Perfect Continuous (Progressive) #8

The past perfect continuous is also known as Past Perfect Progressive Tense, and is used for an action that began before a certain point in the past and continued up to that time. 
Time reference is found in these sentences which gives an idea that action has continued from some time.
Examples:

At that time he had been writing a book for two months.
When she came to the university in last summer, her biology Lecturer had already been teaching there for five years.