Caption: A reference frame laid over spacetime (space and time considered jointly).
Spacetime is a common jargon word in special relativity and general relativity: i.e., in relativity speak.
The clocks illustrate the time dimension.
Credit/Permission: User:Maschen,
2012 /
Public domain.
Image link: Wikipedia:
File:Reference frame and observer.svg.
Local file: local link: frame_reference_spacetime.html.
File: Relativity file:
frame_reference_spacetime.html.