This horn is a compensating double horn. A full double horn is set up so that it has full length valve slides for the F and Bb horns, while a compensating double is set up with full length valve slides for the Bb horn only. On the F side of the instrument, the sound waves travel through the Bb slides plus smaller slides that add enough length to produce the appropriate pitch for the F horn.
Compression reads a perfect score of 0. Comes with fixed bell case