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Hi Dawn,
To ensure that Z coordinate in the drawing will stay always 0, you have to:
- draw everything in XY plane of WCS or in XY plane of UCS which is rotated relative to WCS without changing Z direction
- always check ELEVATION system variable which has to be 0
- use FLATTEN command in XY plane of WCS in "third-party" drawings just after you receive them
- if you have full (not LT) AutoCAD, set OSNAPZ system variable to 1 each time you start AutoCAD (this sys var is not saved between AutoCAD sessions)