largest sounded at the standard pitch of the time, something like a'=415 Hz, while smaller virginals were pitched a tone, 4th, 5th, 8ve or a 9th higher. Some virginals were built as double instrument, with a normal-pitch instrument combined with one pitched an octave higher; this was known as 'the mother with the child', marked 'M' (Moeder) and 'k' (kind) as the smaller instrument was normally stored in a space beside the keyboard of the larger. The actions combined when the octave instrument was fitted on top of the regular one, enabling the musician to play both at once. They occasionally built other compound instruments, fitting a virginal into the empty space left by the harpsichord's bentside. Both single and double manual harpsichords made by the Ruckers family had the disposition 8' 4', with each keyboard having a set of jacks for each set of strings. The standard compass of the Ruckers keyboard is from short octave C/E to c''' or d'''. Double manual harpsichords had their keyboards uncoupled and aligned to sound a 4th (occasionally a 5th) apart, with the upper manual at standard pitch and the lower pitched below it; when each manual was being used the jacks of the other manual were disengaged. 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. Variations of the standard models were sometimes produced for export to France or England; there are single manual harpsichords with chromatic basses (rather than the short octave) down to C, probably intended for England, and double manual harpsichords with a lower-manual range of GG to c''' and an upper manual range of F to f''', produced for France, the lower manual being at standard pitch and the upper a 4th below, reversing the usual pitch arrangement. The lower manual range of these instruments suits the music of contemporary French harpsichord composers such as Chambonnières and Louis Couperin, while the upper manual range is close to early French organ design. When constructing an instrument, a number was written on the case and many of the parts of the action, along with a serial number depending on the model. This has let researchers learn much more about undated instruments and helped them estimate the rate of production—calculated at up