Physical reading rulers are simple yet effective interventions that help readers with dyslexia. Digital reading rulers may offer similar benefits. Given their potential value, we provide the following contributions: (1) We host focus group sessions including people with dyslexia to build upon their lived experiences, (2) We provide evidence for designs that are effective and preferred, (3) We measure reading gains of rulers for readers with and without dyslexia. Using inclusive design principles, we arrive at four digital ruler designs - Grey Bar, Lightbox, Shade, and Underline. For the first time, we offer a comprehensive evaluation of digital ruler effectiveness on 91 crowdsourced readers with dyslexia and 86 without. Considering reading speed, comprehension, and preference, many readers benefit from these rulers, with the largest gains among readers with dyslexia. Rulers designed by readers with dyslexia increased the reading speeds of readers with dyslexia, supporting the need for inclusive design practices.