I would probably voice it in the 'ask for clarification' way with a time delay to give the teacher time to process it.
So for something that was a sensitive issue, I'd say something like, *raises hand* "While we are on this topic, I had heard something xyz on the internet and wanted to get your thoughts on it. I don't want to take up the class time, but is there a better time I can talk with you to find out more about resources on xyz that you feel are credible?"
For something more simple, like silk weights, I would probably just say it more openly, *raises hand* "I read that silk weights are usually measured in mommes. Is that the same thing?"
I think that most people tend to be more open and less confrontational about their beliefs when something is asked as a question, especially when the asker is also staying open to the answer.
Being open to the answer is key. I have heard a story of a student 'correcting' a master workshop instructor from Egypt about 'what they do in Egypt.' I would find that incredibly frustrating as both a teacher and a student, so I would always recommend phrasing it as a question and being open to hear the teacher's response.
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