Standard deviation is the square root of variance, but variance is given by mean, so divide by number of samples. That is : 38.5/10 = 3.58. But standard deviation equals the square root of variance, so SD = the square root of 3.85 which is 1.96.
The virginal(s): The virginal, also called virginals, usually has a rectangular case with the keyboard across the wide side. As with the spinet, the strings run side-to-side relative to the player. Again, it saves on wallspace, and again they rate their own FAQ. Virginals were fairly early, 15th and16th centuries.
The 'una corda' is notation for the soft pedal. The soft pedal is common in post-Classical works, such as compositions by Beethoven or Chopin. Its melodramatic tone enhances soft passages, but it is important to know the difference between playing with the dynamic marking piano and with the soft pedal.