def measure_size_drift(self, z, size=<NUM_LIT>, zoffset=<NUM_LIT:0.>):
drift = <NUM_LIT:0.0><EOL>for i in range(self.measurement_iterations):<EOL><INDENT>psf, vec = self.psf_slice(z, size=size, zoffset=zoffset+drift)<EOL>psf = psf / psf.sum()<EOL>drift += moment(psf, vec[<NUM_LIT:0>], order=<NUM_LIT:1>)<EOL>psize = [moment(psf, j, order=<NUM_LIT:2>) for j in vec]<EOL><DEDENT>return np.array(psize), drift<EOL>
Returns the 'size' of the psf in each direction a particular z (px)