History & Origins of the Standard Tuning for Guitar - Guitar Fretboard Knowledge
Guitar tunings - Wikipedia
guitar | History, Types, & Facts | Britannica
How to Tune a Guitar | Sweetwater
Guitar Strings Order: How to Tune a Guitar and Why | Stringjoy
Guitar History: How the Guitar has Evolved | Musicians Institute Hollywood
History of the Guitar - Evolution of Guitars
The tuning boards of a Gibson Harp Guitar, (Circa 1800) is seen on display as part of a new exhibition from the National Guitar Museum "Guitar: The Instrument That Rocked The World"