Ronchi ruling

A Ronchi ruling or Ronchi grating, named after the Italian physicist Vasco Ronchi, is a constant-interval bar and space square wave optical target that has a high edge definition and contrast ratio. Ronchi rulings are commonly manufactured through photolithographic deposition of chrome on glass or optical substrates. Ronchi rulings are used for optical testing purposes, e.g., the Ronchi test and as scales for a linear encoder.