A popular refinement replaces the analog dial with an electronic digital display that displays the reading as a numeric value. Rather than a rack and pinion, these calipers use a linear encoder. Some digital calipers can be switched between centimeters or millimeters, and inches. All provide for zeroing the display at any point along with the slide, allowing the same sort of differential measurements as with the dial caliper. Digital calipers may contain a "reading hold" feature, allowing the reading of dimensions after use in awkward locations where the display cannot be seen.