Why do some scopes have a single sided chestpiece, others a two sided chestpiece, and still others detachable chestpiece fittings?

Generally speaking, to attenuate certain frequencies. The flat side is equipped with a membrane that is generally referred to as the diaphragm side. The conical or bell shaped side is called the bell. Body sounds generally fall within a frequency range of 50 to 2000 Hz. The diaphragm side is designed to attenuate the lower frequency and accentuate higher frequencies within this range - from 500 to 1000 Hz. The bell side is designed for lower frequencies - from 50 to 500 Hz. Most diaphragm only scopes (ADC 660, 662 and 665 series) are designed for general assessment or blood pressure measurement. Combination scopes (those equipped with both a diaphragm and bell) are designed to provide a broader frequency response. In a typical combination scope, only one side of the chestpiece is "active" at a time. Rotating the chestpiece around its valve stem selects one side and "deactivates" the other. It should be noted that on better quality models there is little or no acoustic leakage from the "deactivated" side.  Our top of the line ADSCOPES with AFD technology allow adjustment of the frequency by altering pressure to the chestpiece.  Light pressure accentuates lower frequencies, while firm pressure accentuates higher frequencies simulating the diaphragm and bell sides of a two sided chestpiece.  ADC offers AFD technology in ½ dozen models ADC produces over a dozen different models of combination scopes with an MSRP from under $2 to nearly $300.