Examples of Counting Shivah Neki'im
Sarah begins counting her seven blood-free days on Monday. On Wednesday morning, she finds a brown stain on the bedikah cloth and brings it to a rabbi. She does not receive an answer before sunset, so she does her usual bedikah Wednesday afternoon and keeps in mind that this may turn out to be a new hefsek taharah. That bedikah is clean. On Wednesday night, the rabbi calls to tell her that her morning bedikah was not good, so that she needs to begin counting again. Sarah can count her Wednesday afternoon bedikah as her new hefsek taharah. Her new shivah neki'im will thus begin on Thursday, and she may immerse in the mikveh the following Wednesday night.
Rivka begins counting her seven blood-free days on Monday. On Wednesday morning, she finds a stain on her white underwear. She decides that she has definitely invalidated her shivah neki'im and puts on colored underwear. Later, a friend suggests that she show the stain to a rabbi. She does so, and the rabbi rules that the stain does not in fact invalidate her shivah neki'im. However, since she made a definite decision not to continue counting, she must perform a new hefsek taharah and start counting over again from the beginning.