I made this years ago for some long-forgotten project but it's proved useful a few times since then.
Inevitably, there will be situations where you simply can't get a six inch scale 'in there' to measure something. My solution was to cut a scale into a number of pieces of different lengths and make a simple pinch clamp holder for the pieces.
I wasn't doing anything requiring high precision so I used a plastic scale. I suppose one could make a precision version by cutting up a steel scale and using a surface grinder to bring the pieces to size.