I don't know but I'm hard of hearing and I like people to observe the following rules.
1. Don't use your hands to emphasize a point. It distracts me. You can however use your hands to show how big something is.
2. Don't shout at me. It doesn't help that much.
3. Don't run your words together. I find Eastern Canadians coming from Ontario almost run their words together they speak so quickly. I can't make out more than 1/2 of what they are saying.
4. Look directly at me and be in front of me.
5 Don't wave your head around like a flag. That's very distracting..
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If you're testing someone for deafness, sit with your back to them. Tell before hand what you are doing. You're not being rude. It's just a test.