Could you please tell me when do we use "Do you mean...?" vs. "Did you mean...?"?

I understand we use this phrase to make sure we understand what someone has said. What I'm confused about is when someone said something, it means he meant something. I would say this should always be in simple past tense, that is "Did you mean...?", shouldn't this? I know I'm wrong, though. Kindly explain.

Please feel free to edit my post for any grammatical errors. I am eager to learn.

Thanks in advance for your clarification. Emotion: smile
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Comments  (Page 2) 
That makes more sense to me now. Thank you so much, Michal. Emotion: smile
No problem. Emotion: smile I'm glad I helped.

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I will do as you say. This is indeed a great forum to improve one's English especially for non-native speakers like me. Emotion: smile