Last night I was trying to play along with an old Buddy Guy song but I was having trouble finding the key. I finally found that the main box pattern started at the 10th fret. I had never used the main pattern starting that high on the board, so was unsure what key it was. I checked the guitar scale system software and found it was D. Later that night I realized I was not clear on what determines the key for the pentatonic scale.
When I woke in the morning the first thing that came into my mind was that the key of the scale is determined by where the main pattern begins on the 6th string. What confused me is why the main pattern is the determinator of the key, why not any of the 4 other remaining patterns? Counting up the 6th string to the 10th fret I found the D note, so I now have a solid idea of what determines the key.
Today I felt ready to expand my knowledge of the blues, so I googled "12 bar blues progression" and was led to Olav Torvund's site. There was a clearly written article on the basics of blues chords, and I practiced along with the example of E, E7, A7, B7. I was surprised how good it sounded - my strumming and chord changing skills are increasing, along with my knowledge.
