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.
They might have derived from shields and are still made of bronze alloys. Wood is the secret of stringed instruments such as violins, violas, cellos, double basses as well as pianos and guitars. They might have derived from bows and arrows.