Aliquot means “divisor.” This refers to Blüthner’s string plan, patented in 1872, which has a fourth string for each note above the tenor range, not struck by the hammer and tuned an octave higher than the strings which are struck. The purpose was to reinforce the treble, and/or to make the sound more complex and interesting. Several other mid-nineteenth century piano makers experimented with this basic idea in different ways, and Steinway’s execution of this concept, which they called “duplex stringing,” is a part of the design of most modern pianos.
The Aliquot Grand system was available on Blüthner pianos as an option for decades. However, this piano is almost unique in another way: although it has a full cast iron plate, and is technically cross-strung or overstrung like the American pianos which were so influential at the time, it is basically a straight strung piano because the bass bridge is more or less in the position it was on the earlier European pianos.