> String instruments are tuned by pure intervals across the open strings
Depending on what you mean by a 'pure interval,' it might come as a surprise that string instrumentalists tend to tune their fifths narrower than 3/2 (and apparently sometimes narrower than a 12-EDO perfect fifth!). This is so the perfect fifth above the highest string is tuned correctly as the major third (and some octaves) above the lowest string. Otherwise, the interval would be a Pythagorean major third (81/64) which is somewhat dissonant.
(In "How Equal Temperament Ruined Harmony," Duffin recounts how in the late 1800s, even the best piano tuners in Britain were unable to get exact equal temperament, being off by about 1 cent per note in such a way that favored common keys. And, even so, equal temperament for pianos was not popular until the 1910s -- non-equal temperaments were favored due to their sound rather than just their practicality.)
I'm not surprised at all. I was taught to use perfect intervals myself, and it's how I've always seen it taught. But tuning is a very interesting topic.
These days I play double bass in a jazz band, so of course every single instrument has its own tuning quirks.
An amusing anecdote: I played in a band, and the drummer complimented my intonation. I asked him how a drummer knows anything about intonation. He said: "My college major was trombone."
Depending on what you mean by a 'pure interval,' it might come as a surprise that string instrumentalists tend to tune their fifths narrower than 3/2 (and apparently sometimes narrower than a 12-EDO perfect fifth!). This is so the perfect fifth above the highest string is tuned correctly as the major third (and some octaves) above the lowest string. Otherwise, the interval would be a Pythagorean major third (81/64) which is somewhat dissonant.
(In "How Equal Temperament Ruined Harmony," Duffin recounts how in the late 1800s, even the best piano tuners in Britain were unable to get exact equal temperament, being off by about 1 cent per note in such a way that favored common keys. And, even so, equal temperament for pianos was not popular until the 1910s -- non-equal temperaments were favored due to their sound rather than just their practicality.)