Scale is the most important one for the end user ( construction type worker). In almost 100 % of cases, the scale is described right on the drawings and even sometimes, a ruler or sample scale provided somewhere on the documents( think of a map - same concept). A group of drawings may have many different scales, so each page must be checked carefully. That and the ability to convert metric to imperial when required. other than that, calculations have been done at the design/engineering phase, usually aided by computers.