The Fitting Standards govern what values are used for various dimensions, seams, joints, and so on when fittings are taken off. You can set them up however you want: to be entered at takeoff time, to be calculated by a formula, based on another value, or a standard value.
In Fitting Standards, you can set-up how you want to takeoff the fabricated fittings. You will choose the order of the dimensions, how they behave (whether they are always prompted for a value, whether it repeats a value, etc.), and how the accessories (vanes/joints/etc.) behave.
Other topics discussing Fitting Standards include: