Past continuos: The past continuous tense is used in sentences with two past actions to show that, while one action was going on, another action occured.
example: While I was taking a bath, the telephone rang.
obviously, the past continuous describes the longer action, and the past tense describes the shorter action. (while and as are often used with the past continuous form.)
Also, the past continuous is often used in connection with the preceding statement and also in response to a question.
example: She didn't want to interrupt him. He was counting the receipts.
"Where were you last night?" "I was in the library reading."
Present perfect continuous: The present perfect continuous emphasized the continuing sense of the action from an earlier time to the present.
Example: It has been raining in London since our arrival.
also, there isn't a huge difference between present perfect and present perfect continuous when the intent is to: express continued action from the past to the present. Therefore, it is also correct to say: It has rained in Londong since our arrival.
Note: Still, "Length of time" is either mentioned or implied with present perfect continuous.