With Martin model designations, the digit before the hyphen corresponds to body size and the bigger the number the smaller the body. So, when the 0 (usually pronounced ‘oh’ despite it being an ‘aught’) was first introduced in 1898, it would have been considered a sizeable guitar.
It was second only to Martin’s 00 model, which was introduced the same year and remained Martin’s biggest model until the arrival of the 000 in 1902.
