Calibration in temperature of the position of sources along the principal curve fit in the 3D space comprised of the two first diffusion map coordinates and the absolute magnitude, M_G. The position along the curve is parametrised with λ and artificial scatter is added to help visualize the number of sources used. Black points represent sources with effective temperatures derived from high-resolution spectra and GUCDS standards while orange points represent the rest of GUCDS sources.