Technical drawings are any scaled diagrams, blueprints, design outlines, or other scaled drawings produced by designers such as architects or engineers. Their execution should be of extremely high quality, suitable for use in building, repair, redesign, and any necessary tasks requiring exact knowledge of specifications.

There are three main cautions in the use of technical drawings as a source. First, it is important to record their date whenever possible, because plans change and later ones supersede earlier versions. Second, it may be easy to make errors in reading these, as numbers may appear out of context - for example when looking at a linear measurement it is critical to look at both ends of the line, as it might be that neither end is zero. Third, it is important to look for the most detailed sheet of technical drawings, because measurements taken from a general overview (like the elevation sheet) sometimes omit details which affect the measurement.

The drawing must supply construction-quality technical information. A promotional illustration can depict the same design without that precision. Reading the dated and sufficiently detailed drawing is necessary to distinguish a documented dimension from an inference based on the picture.