PaulTheCAD's (Paul Tracey) - TurboCAD Tips: Snap Angles

As a default, by holding down the Shift Key you can restrict drawing a line to 90 degree increments. (Horizontal or Vertical). This also goes for rotating a rectangles, or other polygon etc. You can edit this 90 in the Angle dialogue box under OPTIONS – Angle, to jump to any number of degrees.

You’ll also note that you can change the base angle from where you start drawing from, especially useful if you are drawing a line of objects at an angle not perpendicular to the sides.