In this paper, design variations and influence on drawings in building projects are clarified. Therefore, the building projects carried out continuously by Design/Build Contract is adopted, and statistically analyzed the design variations by the drawings & specifications and the records of the building projects. Result as follows. Many of contents in design variations were not major changes about the whole building, but minor changes about the room arrangement and the finish material and equipments. And 14% of design variations in the implementation stage were not made into subject about the contents, and drawings & specifications were not shown in the design stage. And floor plan tends to be influenced of design variations. And the designer should be careful to explain about the room arrangement and the height &width of the door in detailed floor plan & interior elevation, and about the electric facility in the equipment drawings.

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It is of importance to define the suitable project system of an oblique projection drawing whose projection principle is different from that of human eyesight, while the limit of cognizing an oblique drawing causing misunderstanding is not generally definite. The adequate or allowable direction and scale of a cube on an oblique projection drawing were discussed based on cognizing tests, considering that an oblique projection drawing is distorted from an axonometric projection drawing in the present study. Two kinds of tests were carried out ; one is with table displaying drawings in order, and the other is with those at random by parameters θ and φ . The tests reached the limit length ratio g'<28%, which is deeply correlated with the distortion and it was concluded that with the adequate or allowable projection system one should draw the three surfaces of a cube equally under satisfaction of the limit length ratio. The corresponding parameter set is in the domain from «θ =60° φ =30° » to «θ = 70° φ=45°». The tests suggested the tendency to feel the drawings with the glance from high position less practical, and the random display tests showed the directivities depending on the characteristics of the subjects.

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