The probable error of a single observation is calculated from the equation ______.
1
\(\rm Es=\pm0.729\sqrt{\Sigma r^2}/n-1\)
2
\(\rm Es=\pm0.6745\sqrt{{\Sigma v^2}/n-1}\)
3
\(\rm Es=\pm0.6745\sqrt{\Sigma v^2}/r-1\)
4
\(\rm Es=\pm0.943\sqrt{\Sigma v^2}/n-1\)