Unusual types of gramophone records Sievey. Chocolate records about three inches in diameter, and small players made for them, were marketed as a novelty in Europe in 1903–1904. After a record wore out or ceased to amuse, it could be eaten. In 1973, the Kingdom of Bhutan issued several unusual postage stamps that are playable miniature phonograph records. These thin plastic single-sided adhesive-backed 33 RPM discs feature folk music and tourism information. Not very practical for actual postal use and rarely seen canceled, they were designed as revenue-generating novelties and were initially scorned as such by most stamp collectors. Their small diameters (approximately 7 and
Hydraulic diameter also used in calculation of heat transfer in internal-flow problems. For a fully filled duct or pipe whose cross-section is a regular polygon, the hydraulic diameter is equivalent to the diameter of a circle inscribed within the wetted perimeter. Hydraulic diameter The hydraulic diameter, , is a commonly used term when handling flow in non-circular tubes and channels. Using this term, one can calculate many things in the same way as for a round tube. It is defined as where More intuitively, the hydraulic diameter can be understood as a function of the hydraulic radius , which is defined as