I am 66 years old and am retiring at the end of the year. I decided to return to playing guitar, which I dabbled in as a teenager. I bought myself a Martin LXK2 guitar right here. ( Beautiful 3/4 sized instrument made of HPL with beautiful tone and projection. No humidity worries and a sustainable product as it's made of recycled materials. See my review) It was $280 well spent. I opened the bag, tuned the guitar and to my delight, my aging brain had retained chord after chord: G, C, C7, D, A, A7, E all came back along with the string names E, A, D, G, B, E! Determined to build on this antique knowledge, I searched for a convenient chord book, and see that the reviews I read did not lead me astray.
In an acoustic instrument, the body of the guitar is a major determinant of the overall sound quality. The guitar top, or soundboard, is a finely crafted and engineered element made of tonewoods such as spruce and red cedar. This thin piece of wood, often only 2 or 3 mm thick, is strengthened by differing types of internal bracing. Many luthiers consider the top the dominant factor in determining the sound quality. The majority of the instrument's sound is heard through the vibration of the guitar top as the energy of the vibrating strings is transferred to it. The body of an acoustic guitar has a sound hole through which sound projects. The sound hole is usually a round hole in the top of the guitar under the strings. Air inside the body vibrates as the guitar top and body is vibrated by the strings, and the response of the air cavity at different frequencies is characterized, like the rest of the guitar body, by a number of resonance modes at which it responds more strongly.

Russell, George (2001) [1953]. "Chapter 1 The Lydian scale: The seminal source of the principal of tonal gravity". George Russell's Lydian chromatic concept of tonal organization. Volume One: The art and science of tonal gravity (Fourth (Second printing, corrected, 2008) ed.). Brookline, Massachusetts: Concept Publishing Company. pp. 1–9. ISBN 0-9703739-0-2.
In 1977, the Guitar Institute of Technology (GIT) revolutionized contemporary music education with the first full-time program to offer hands-on professional training for the electric guitarist. Over three decades later, MI remains the leader in guitar education, besting other colleges for guitar players, with a unique system that combines technical, creative and professional development in a performance-based program.