Vierne indicates "Fonds et anches" for the Récit expressif manual, and "Fonds et anches, et principals" for the Positif, Grand, and Pédale manuals. The Westminster tune within the piece is played on the Positif and Récit coupled, so as to give the theme substantial prominence over the pedal and harmony lines. The supporting secondary theme (rapid eighth and sixteenth note groupings against the dotted-quarter note primary theme) opening the piece is given less registration and seems to bubble along, weaving in and out of its strong namesake theme. Stops are added little by little throughout the piece, gradually building up to the climax using full organ and a fully open swell box (precise stops to be determined by performer and his or her organ). Vierne understood similar flexibility with regards to how fast the piece should be played, articulation, and phrasing. Vierne never wrote metronome markings on his manuscripts; he knew that a piece played in a small drawing room could not be played at the same tempo in a cavernous stone cathedral. Whatever tempo chosen should be strictly adhered to throughout the entire piece. Articulation between phrases is also determined by the venue. For performance of "Carillon de Westminster" at Notre Dame, breath between phrases would have to be longer in order to remain clear than in a smaller setting. The French-Romantic tradition emphasizes legato playing. The right-hand is split into one-bar phrases but it is not clear whether this was intended by Vierne (his manuscripts are notoriously difficult to read due to his sight). The same clarity pertains to the rest of the piece, especially the chord progressions at the end after the climax. Such thick chords can sound muddy if not played with precise, even attack and release. In some venues it would be wise to shorten the value of each chord slightly, and insert a 32nd rest between each one.