Instrumental drawings are different from freehand drawings (see above), although they are usually the result achieved through the development of ideas using freehand drawings (including sketches). Freehand drawing and instrumental drawing differ primarily in the amount of time and accuracy required - freehand drawing is a means of quickly putting your thoughts down on paper without the use of instruments such as rulers, set squares and compasses. So, in appearance, the freehand drawing is entirely different from the clean-cut precision of a mechanically ruled or computer generated instrumental drawing.
Instrumental drawings sometimes referred to as technical drawings, mechanical drawings or working drawings require the use of manual (using drawing instruments examples from the past ) and/or electronic drawing methods. They are often orthogonal (also referred to as 'orthographic') drawings, but may be paraline drawings such as isometric, oblique and planometric drawings - usually used as 'support' drawings showing a 3D view of the object shown in orthogonal/orthographic drawings.