I know it is an O-Scope and when I hook 12 VDC to it I get the straight green line across the screen and if I touch one of the probes the line jumps.
I am guessing it was made by SUN or Snap-On as the tag is missing.
I think it plugs into a test box of some sort.
Is this what SUN had before they came out with Ignition scopes?








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