but revolves around a different harmonic progression. Sousa then uses his trademark chromatic-accented chord A♭7, (a half-step below the previous chord) to create a "wall of tension" that quickly resolves into the I chord. Another chromatic-accented chord change often used by march music composers is inverting a I chord with a lowered third and raised fifth. For example, an E major chord (the I in the key of E) would be followed by a B major chord, (which is an E chord with a lowered third and raised fifth). Unlike secondary or "borrowed" dominants, this chord does not have logical harmonic functions other than to add texture and interest. Difficulty of performance The actual difficulty of performance varies considerably among marches. When first being written for grade school bands then being organized throughout the country, most marches were fairly modest in difficulty. Soon however, there were composers writing scores for (their own) bands that required professional to almost virtuosic skill to perform—some composers noting that any given march might be difficult to play "perfectly", that is, with all the correct expressions and articulations and with steady tempo. A grading system of difficulty of performance as adapted from Norman Smith's "March Music Notes" follows. Grade 1: Minimum difficulty. Suited for beginner bands first approaching music; may be a simple etude or ditty from an instructional book. Grade 2: Also for beginner bands, but more developed, using different notes and rhythms. Instrumental ranges are comfortable, most requiring minimal endurance. Some scores follow the standard march form, but most are abbreviated, or of a simpler concert march form. Grade 3: At standard march difficulty. Usually in full march form, and requiring moderate technique and endurance skills. Instrumental ranges are usually intermediate, and likely containing chromatic notes, obbligatos, and counter-melodies. Many parade marches contain Grade 3 scoring, examples being "The Thunderer" and "The National Emblem". Grade 4: Moderately difficult, containing many technically challenging parts and some syncopation. This grade requires a considerable amount of practice/rehearsal of most high school bands; and typically requires a disciplined, complete ensemble for proper performance, as it contains intricate harmonies and counter-melodies. Example scores of this difficulty are "The Stars and Stripes Forever" and "Barnum and Bailey's Favorite". Grade 5: Considerably difficult; usually originally written for professional or virtuoso players such as those in a circus band, as screamers are typical of this grade. Grade 5s contain woodwind obbligatos