User talk:70.172.9.13

January 2022
Hello, I'm DVdm. I noticed that you added or changed content in an article, Doppler effect, but you didn't provide a reliable source. It's been removed and archived in the page history for now, but if you'd like to include a citation and re-add it, please do so. You can have a look at referencing for beginners. If you think I made a mistake, you can leave me a message on my talk page. Thank you. DVdm (talk) 19:48, 17 January 2022 (UTC)