Past simple to express a point in the past

The past simple is used to refer to a point in the past at which another event was in progress, had been completed or had been going on for some time. The past simple thus serves as a time marker in subordinate time clauses within complex sentences, where the main clause is in the past continuous, past perfect or past perfect continuous tense:

When I called her, she was studying.
By the time we reached the top, it had stopped raining.
When I got to her house, she had been waiting for hours.