503 and directed to 515 a command of ed electrical drafting would be directed to 509 upon the first d ductwork entry the system looks to see if a duct point has been established as shown at d1 in fig2 this duct point is established as the leftmost point on a starting duct line drawn horizontally or the bottommost point on a starting duct line drawn vertically this line represents the starting end or width of the duct to be drawn in direct combination with the duct point is an axis of direction similar to the points of a compass referred to in degrees zero degrees is straight up 90 degrees is to the right 180 degrees is to the bottom etc this establishes duct direction from the starting point initially the absence of a duct point will cause the system to request this information and the axis of direction as shown at d2 thus establishing a starting point on the crt display which is then displayed against the background of the building structure as fed to the computer during execution of programs 401 and 402 following this step the system will request figure identification at d3 which are the four basic figures t o b e and a straight section j these correspond to transition offset bevel elbow and joint straight section additionally the operator can enter h a l f and d corresponding to head or duct cap access door an l angle frame a flexible connection and a damper fire damper volume damper etc these are standard duct accessories.