Mechanical building services (plumbing, heating, ventilation, and air conditioning systems) generally are shown on backgrounds of architectural floor plans and are set up for plotting scales of 1/8" = 1'-0" (1:100), 1/4" = 1'-0" (1:50).

1. Set drawing units for imperial to architectural, with precision set to 0. For metric, use decimal with precision set to 0.

The reason is that mechanical systems are shown graphically with nominal sizes that are not intended to reflect the actual size of a pipe or duct and are generally located relative to building components with a tolerance of plus or minus 6" (1:50). Using a precision set to 1/16" or 10 mm serves no practical purpose.

2. Set the drawing snap to On, with a value of 1" for imperial and 25 mm for metric. This way, you will always be able to hit the end point of a line without a snap override.   

Notes from Cadalyst tip reviewer R.K. McSwain: Different drafting disciplines require different standards. Here, Dave shares his recommendations for working with mechanical systems.