The standard deviation is the square root of the variance. Given that the variance of the data set is 12, you can calculate the standard deviation as follows:
\[ \text{Standard Deviation} = \sqrt{\text{Variance}} = \sqrt{12} \]
Calculating that:
\[ \sqrt{12} \approx 3.46 \]
Therefore, the standard deviation of the data set is approximately 3.46.