Prior to about 1910 the A440 standard to which modern musical instruments are tuned did not exist. The instruments produced before A440 became standard were tuned to a pitch that, in saxophones, at least, is approximately one semi tone (half step) above a modern sax. That is why the modern saxophone is designated Low Pitch and the others designated High Pitch. Since tube length determines pitch, these High Pitch saxophones are, by definition, shorter in total tube length than their modern counterparts. In general, the tube length of High Pitch saxophones is about 10% less than for their modern, Low Pitch counterparts. Until the early 1930s some of the USA sax builders still offered High Pitch instruments as part of their regular line. During the period when both High and Low pitch instruments were commonly produced by the instrument makers, it was necessary to mark each instrument as to what pitch it was tuned. Fewer and fewer high pitch saxophones were produced as time went by, and in the 1930s the high pitch models became completely obsolete. When it was no longer possible to buy a new high pitch sax, the need to mark each instrument was no more, and the manufacturers stopped marking the Low Pitch instruments at that time. There were not many High Pitch horns made in the later years, but there obviously were some. It pays to be certain unless you are a collector of the odd or obscure.
The notion of a standard of pitch has been an issue for instrument makers for many centuries. Today, we assume that instruments are built to a pitch standard of A=440, but this was not always the case. 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. 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).
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 466).
Woodwind instruments have a long, thin column of air. The lowest note is played with all the
tone holes closed when the column is longest. The effective length is changed by opening and
closing finger holes or keyholes along the side, all holes closed gives the lowest note and
opening the holes successively from the bottom end gives a chromatic scale. The distances
between holes are proportioanal to the length of the column of air. These proportions are
different between low- and high-pitched instruments. It is for this reason that, while a
musician playing on a high-pitched instrument may be able to tune one note with others playing
low-pitched instruments, he will still be out of tune with the group when playing other notes.
The distances between the holes cannot be changed in either case. There is no satisfactory way to
shrink or stretch an instrument made of wood or metal.