Complex sentence: The Ruckers double manual harpsichord thus worked as two instruments in one, pitched a 4th apart, a use very different from that of later two-manual harpsichords, whose keyboards were designed to be played together or antiphonally at the same pitch, for timbral contrasts.
Split into simpler sentences: The Ruckers double manual harpsichord thus worked as two instruments in one, pitched a 4th apart. Later two-manual harpsichords keyboards had the two sets of strings tuned together or antiphonally at the same pitch, for timbral contrasts.