present and past perfect continuous tense

We use the Present Perfect Continuous to show that something started in the past and has continued up until now. "For five minutes," "for two weeks," and "since Tuesday" are all durations which can be used with the Present Perfect Continuous.

1. They have been talking for the last hour. 
2. She has been working at that company for three years. 
3. What have you been doing for the last 30 minutes? 
4. James has been teaching at the university since June. 
5. We have been waiting here for over two hours! 
6. Why has Nancy not been taking her medicine for the last three days? 

We use past perfect continuous tense to show that something was started in the past. "For five minutes," "for two weeks," and "since Tuesday" are all durations which can be used also with the Past Perfect Continuous.

1. They had been talking for the last hour. 
2. She had been working at that company for three years. 
3. What had you been doing for the last 30 minutes? 
4. James had been teaching at the university since June. 
5. We had been waiting here for over two hours! 
6. Why had Nancy not been taking her medicine for the last three days? 

You see in above both type of sentence that some changes are done. Actually the sentences are same but their existence change.
For example the sentence is same only it changes its state from present to past. In present perfect continues tense has been and have been are used. With singular has been are attached and have been are attached with plural. And in past perfect continuous tense had are replaced by has or by have because the work is doing and done in the past.