I don't know what they mean when they say some trombone reads regular bass clef in C. Afaik all their instruments are transposing Bb Eb etc. Their part is written in a different keys from the C instruments so it all sounds the same. We used to have a trombone player from a orchestral background who was having to transpose in his head to play the written big band parts. Why do I care? We are short of trombonists and long on bassists and I always had a hankering to play one. But the idea of reading in a different key leaves me cold as I have been progressing in my limited ability to sight sing my bass parts. I wouldn't like to stuff that up. How's that working for all the tuba doublers?