Here's a Fab Lab Skill Builder video tutorial on how to use a dial test indicator to locate the center of a square or rectangular workpiece.

  Swing Indicating may be "old hat" to more than a few readers of this blog, but we find in our CNC Fundamentals Workshops that many new and self-taught machinists have never used the technique before.  Here's a brief Fab Lab tutorial on how to indicate the center of a hole.