Unusual types of gramophone records Unusual types of gramophone records The overwhelming majority of records manufactured have been of certain sizes (7, 10, or 12 inches), playback speeds (33, 45, or 78 RPM), and appearance (round black discs). However, since the commercial adoption of the gramophone record (called a phonograph record in the U.S., where both cylinder records and disc records were invented), a wide variety of records have also been produced that do not fall into these categories, and they have served a variety of purposes. The most common diameter sizes for gramophone records are 12-inch, 10-inch, and 7-inch. Early American shellac records were
Quadratic mean diameter timber in a forest, because it has the practical advantage of being directly related to basal area, which in turn is directly related to volume. QMD can also be calculated as: formula_3 where BA is stand basal area, n is the number of trees, and k is a constant based on measurement units - for BA in ft and DBH in inches, k=0.005454; for BA in m and DBH in cm, k=0.0000785. Quadratic mean diameter In forestry, quadratic mean diameter or QMD is a measure of central tendency which is considered more appropriate than arithmetic mean for characterizing the group