good points all about use of the slide, especially on retuning as the session progresses....flutes warm up and pitch sharpens. Tune to the accordion.....they'll usually be right on.....then the guitar, then the fiddle, as choices.
anyway.....remember the science, too, by Rudall&Rose that with every change of the slide, so, too, must the cork change. As the slide moves inward, the cork moves backward in an amount about 20% of the movement (this is totally approximate). Outward slide, inward cork.
It's best shown on their Patent Head....terribly heavy (although beautiful) but the science and engineering of one is gorgeous. No one applies this now, but should, frankly.
Greg Collins has a Patent Head....I'm sure he'll chime inhere with a word or two.
