 While technical improvements and an equal-tempered scale reduced the need for two clarinets, the technical difficulty of playing in remote keys persisted, and the A has thus remained a standard orchestral instrument. In addition, by the late 19th century, the orchestral clarinet repertoire contained so much music for clarinet in A that the disuse of this instrument was not practical. Attempts were made to standardise to the B ♭ instrument between 1930 and 1950 (e.g., tutors recommended learning the routine transposition of orchestral A parts on the B ♭ clarinet, including solos written for A clarinet, and some manufacturers provided a low E ♭ on the B ♭ to match the range of the A), but this failed in the orchestral sphere.
