User talk:Chenming20090728

July 2019
Please refrain from making unconstructive edits to Wikipedia, as you did at Global Positioning System. Your edits appear to constitute vandalism and have been reverted. If you would like to experiment, please use the sandbox. Repeated vandalism may result in the loss of editing privileges. Thank you. - DVdm (talk) 13:36, 15 July 2019 (UTC)