|For reasons that have been widely debated, the Ruckers
built their two-manual harpsichords in a transposing configuration, with the
lower manual shifted a fourth below the upper, both playing the same strings.
These instruments were important in the history of the harpsichord, as they were the first double manuals, and they were almost all (three known exceptions) refashioned into contrasting double harpsichords, many in France, where their exceptionally beautiful sound gave direction to the great French schools of building.
This is the 1638 Ioannes Ruckers instrument at the University of Edinburgh.