Whether you’re using the the coordinate box or the tracker, there are a lot of ways to write a number.  Some are easier than others.  A quick rule of thumb is that ArchiCAD recognizes fractions as inches, whole numbers and decimals as feet.  So… a couple of ways to input three and a half inches:

• .2916667′
• .2916667
• 0-3.5″
• 0-3.5
• 3.5″
• 3 1/2″
• 3 1/2
• 3.5/1
• 3.5/
• 7/2″
• 7/2