If you have ribbons you probably want to look into measurement methods that are designed for anisotropic samples such as verticle sectioning and cycloid intercept measurements. Check out more info in this book: The Quantitative Description of the Microstructure of Materials.
why do we need more than one line to determine the grain size?
Is there a problem if angle is not 90°? I have ribbons and straight line across specimen is not perpendicular...
If you have ribbons you probably want to look into measurement methods that are designed for anisotropic samples such as verticle sectioning and cycloid intercept measurements. Check out more info in this book: The Quantitative Description of the Microstructure of Materials.