First, it's helpful to understand what Color Bars and Tone are for. The goal when mastering is to make sure that the image and sound meet broadcast standards, and that you do as much as possible so that your program is viewed and heard outside of your facility just as you created it. In order to do this, we all agree to use a common reference for picture and a common reference for audio. This way, when your film or program is broadcast or duplicated, if there are any deviations from these agreed upon reference values on the Master Tape or Master Digital File, then adjustments can be made, so that the image and audio remain within broadcast specifications as well as are consistent to the levels they were when mastered at your facility.
Before mastering, we start by using Color Bars and Tone to calibrate the equipment in our edit bay/facility. We'd use Color Bars to properly calibrate the external NTSC, PAL, and/or HD monitor that is connected to the editing...