Watch the Open Strings Functioning online guitar lesson by Brad Carlton from Guitar Lab: Open String Universe
All of the chord voicings included in this group of lessons have the root on the 6th string but the 1st, 2nd, and in some cases the 3rd string remain open. The chart presented in this lesson reveals the inverse relationship between each open string and its corresponding bass note. Notice how as the root of the chord ascends chromatically, the numeric analysis of each of the top three open strings descends. Make sure you memorize the enharmonic equivalents:
In the upcoming lessons you will see how this information will serve you not only in analyzing the harmony but also in revealing the scale options.