Ground Zero Indicator
（重定向自GZI）
![Ground Zero Indicator, showing the interior graticules (and the insert at bottom left shows the instrument mounted with its cover in place)](/Images/godic/202501/16/GZI_Composite3010.jpg")
The Ground Zero Indicator, known by the acronym GZI was a specially designed shadowgraph instrument used by the British Royal Observer Corps during the Cold War to locate the Ground Zero of any nuclear explosion.