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 clavichord is a keyboard instrument, like the harpsichord, piano, virginal, spinet, and accordion. It is in the class known as the box zither, putting it also in the company of the dulcimer and autoharp. The main division in clavichords is between fretted and unfretted versions. The clavichord is built in the shape of a rectangle.