"Stop every sentence or two to discuss and make sure you understood everything. ”
“To get the most out of the conversation, record your teacher while he or she talks. Then listen to the recording carefully with your teacher. Stop every sentence or two to discuss and make sure you understood everything. ”
Why does “understand”use the past tense in this sentence?
Thank you in advance.

Question

"Stop every sentence or two to discuss and make sure you understood everything. ”
“To get the most out of the conversation, record your teacher while he or she talks. Then listen to the recording carefully with your teacher. Stop every sentence or two to discuss and make sure you understood everything. ”
 Why does “understand”use the past tense in this sentence?
Thank you in advance.

Answer

I can see your confusion. The sentence sounds all right to my ear but I think that it is because this is a very common way of speaking.  But, I agree that "understand" would be better since the important verbs are commands.

However, since "make sure" is a direct command, the word "understood", in the past tense would make sense, if it was describing the reason to "make sure".  If "understand" is used, it would be the equivalent of the other verbs in expressing a direct command.

This is a hard one to explain.  I hope that I've been clear.  Perhaps someone else will explain it more elegantly.