The notion of a standard of pitch has been an issue for instrument makers for many centuries. Today, we assume that instruments are build to a pitch standard of A=4401, but this was not always the case. In the mid-19th century, as the popularity of bands was beginning to grow, the number of different pitch standards was significant. In the early part of the 19th century, the general pitch standard was as low as A=420 (modern Ab is 415). The standard rose quite dramatically throughout the course of the century so that by the end of the century in some venues, pitch was as high as A=457 (modern Bb is A=466), this despite the fact that a standard of A=435 was established by a French Commission in 1859, and in 1887 this was formally adopted by the Vienna Congress, an international conference on musical pitch.
Many American band instrument makers in the later 19th century followed the general trend of building instruments at a higher standard. By the end of he century, however, the influence of the trend toward low pitch was also evident, perhaps owing to the 1887 resolution by the Vienna Congress. As a result, by the beginning of the 20th century until about 1920, American instrument manufacturers were faced with the dilemma of having to accommodate at least two different pitch standards, which were termed "high pitch" (around A=452) and "low pitch" (around A=440).
The manner by which brass instrument manufacturers accommodated these two standards is most interesting. Some instruments were provided with two sets of main slides or with sleeves which could be inserted in the main slide to lengthen it. Some York tubas are equipped with an extra "doughnut" of tubing, located near the main slide, which can be incorporated into the main slide tubing by rearranging the slides. In each case, the objective is to lengthen or shorten the main slide so that the instrument could be tuned to the appropriate standard. Valve slides, if application could be pulled or pushed in to accommodate the main tuning.
While the practice of manufacturing instruments which could play at two standards was abandoned about 1920, some manufacturers continued to produce some high-pitch instruments for a few years. Eventually, of course, A=440 became the standard.
1A frequency of 440 cycles per second produces second space A natural in the treble clef.