Apparently you have two 3D vectors, each of unit magnitude, el and ee, and you wish to find the angle between them. One formula would be:
e = acos(dot(el,ee));
which gives e in radians. Another formula is:
e = atan2(norm(cross(el,ee)),dot(el,ee));
which also gives e in radians. Furthermore it doesn't require that el and ee have unit magnitude. It is more accurate when e is near 0 or pi where the 'acos' function suffers larger rounding errors.
