Custom compass orientation

I need to create a custom compass orientation for my 3" quad that looks like this:


So the compass is rotated up by about 30o. Does this mean I need something like the following in Vector3<T>::rotate():

const static float sintheta = sinf(radians(30));
const static float costheta = cosf(radians(30));
tmp = x * costheta - z * sintheta;
z = x * sintheta + z * costheta;
x = tmp;

or do I need to use 330?