| "The ‘double principle’ system was a variant of the ‘enharmonic’ system of compensation. Most compensation systems have been designed to operate from the third or fourth valve. This system compensates from the first valve. Valves two and three have two alternative sets of tubing, one shorter and the other slightly longer. If the first valve is not employed, then valves two and three will use their shorter branches. However, when the first valve is in use, the second and third valves will re-route to their longer branches to compensate. "
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