• T-squares are simple pieces of equipment used in technical drawing. Their main purpose is to give a clear, horizontal line for the engineer, graphic designer or artist to use in his drawing. They function by balancing the short end flush against the desk and the long end across it. This keeps the line stable and the drawing clear, crisp and professional. They also have other uses, all of which are associated with their stability.
  
  

Horizontal Lines

• By placing the T-square parallel to the upper and lower edges of the paper, the artist can draw horizontal lines. He does so by simply lining up the T-square and drawing a line along the top or bottom edge of the long end of the "T."
  
  

Vertical Lines

• The same technique can be applied vertically. To do so, the artist needs to place the T-square at the top end of the paper. If done correctly, it will look like a proper T, rather than a rotated T that a horizontal line demands.
  
  Once he or she does so, a vertical line can be drawn the same way as a horizontal line--by following the long edge of the T.
  
  

Other Instruments

• The T-square also has other uses, namely to support other instruments. Technical artists also need to use set squares--triangles--and other instruments to achieve perfectly straight lines at specific angles. Rather than just hold these other instruments on the paper, they can balance them on the T-square, using the T-square's set 90 degree angle and stability to make a perfectly straight line.