 They changed to fit new rules along with the rest of the drum corps hornline, first receiving two vertical (or in this case, slanted for ease of use) piston valves, then 3 and later 4 valves to make the instrument fully chromatic.Equivalent instruments in the key of BB and CC were produced by instrument manufacturers for marching bands who wished to possess the sound of these contrabass bugles, generally regarded as "darker", without losing hornline sonority by having the basses in a different overtone series from the rest of the hornline (or requiring marching tubists to learn another set of fingerings for tuba parts originally written for BB and CC instruments).In the 2000s, contrabass bugles often have three or four valves, as is common on concert tubas.