The origins of NTS (Not To Scale) dimensions date back to drafting on paper. On paper it was often simpler to revise a dimension rather than redraw the correct object with dimensions. Typically a drawing with gross dimensional change would have dimensions with a notation of “NTS”. With the advent of CADD (Computer Aided Drafting) it makes little since to only “fix” a dimension and have the underlying object (lines, circles, arcs, et.) incorrect. One of the major assumptions one makes in dealing with a drawing done in CADD is that it is drawn correctly. The big assumption one has with CADD is “it was created in CADD... it must be right”. I know of an engineering firm that does all drawings on CADD, not because it is “faster” or “more productive”, but because their clients assume the drawings are correct and therefore do not question the accuracy of the drawings and file back charges for mistakes...
What happens if someone is sloppy in the revision process and only changes the dimensions by typing in (over-riding) the new “correct” value. The results of over-ride dimensions can be disastrous. The following scenario points out the need to know what dimensions are real (associative) or fudged (over-ride). Lets say that a widget (a fictitious part) drawing is composed of a 4”x5” rectangle with dimensions. The widget drawing is revised and the rectangle is changed by the designer to be 4”x5 ½”. Instead of the changing the rectangle the CADD draftsperson “X” merely re-dimensions the 4”x5” rectangle to 4”x 5 ½”. The widget drawing is plotted and everyone in the office is amazed by the speed of draftsperson “X”. But all is not well in “CADD-land”... Trouble is brewing... The widget drawing is now inserted as a block in and assembly. DXF files are created for the CAM (Computer Aided Manufacturing) department, based on the geometry of the geometry generated by the widget... OhOh!
 

To make the above scenario fit for your own recipe-for-disaster. Take the above scenario and: Substitute the word Widget with what ever you are creating, i.e. bents, doors, or bearings, et.
Substitute the word assembly with Bridge, House, or Motor et.
Substitute CAM department with supervisor, department head, or client, et.

Q: So how is it possible to overcome the “speedy-draftsperson-X” NTS syndrome?
A: Well one would need a utility that would read the drawing data base and check for over-ride dimensions.

Contract CADD Group has created an NTS checking program (with the aid of custom Programming from Robert Cheek of Maple Creek Programming) to search an entire drawing and place the text string NTS inside every offending over-ride dimension. A FREE version of NTS is available for downloading from this site (click here to download). A Licensed  version ($29.95) is also available by contacting Frank Zander at Contract CADD Group (604) 591-1140