Bill Potts wrote in USMA 17783:
>Dots, pages, pixels, etc. are discrete entities. We count them, but we do >not measure them (at least not in the applications so far cited in this >thread). In the case of dot pitch, we may measure the distance by which the >centers of adjacent dots are separated, but that is not a characteristic of >the individual entity. Dots per cm (or dots per inch) is a resolution-based >specification that is fairly easily visualized. This illustrates the difference between inch/pound and metric ways of expressing measurements. The inch is the smallest common imperial unit of length, the mil or thou is a mechanical engineers' unit. Hence imperial or American screw threads are dimensioned in threads per inch, while metric screw threads are dimensioned by pitch in 0,01 mm or in micrometres. Metric drill diameters are expressed in 0.1 mm, while imperial drills are labelled in binary fractions of an inch, or meningless letters or numbers. In the diameter of wire or the thickness of sheet metal I have specifications for imperial wire, Stubs steel wire, Brown and Sharpe, Washburn medium steel wire, US sheet, S&W American music wire, and Burmingham Stubs iron wire. Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 TEL. 416-486-6071
