rtc nrf51 SDK example matches COMPARE0 only once

In order to learn how to use the RTC0 to handle an event every second, I am debugging the rtc SDK example.

Expectation: The rtc example sets the time to check the counter time at 3 seconds. I expect every 3 seconds. the int_type in rtc_handler() will equal NRF_DRV_RTC_INT_COMPARE0.

What I am seeing: the int_type in rtc_handler() equals NRF_DRV_RTC_INT_COMPARE0 after the first three seconds. Then int_type equals only NRF_DRV_RTC_INT_TICK.

Question: is my assumption correct the COMPARE0 should keep repeating such that there is a match every 3 seconds (in this example)

Question: If not, what is the example missing to do so?

thank you.