The determination of magnetic declination angle entails finding two directions: Geographic North and Magnetic North. This paper deals with the former. The known way to do it by using the Suns' calculable orientation in the sky is improved by using a device based on a WIDIF Diflux theodolite and split photocells positioned on its telescope ocular. Given the WIDIF accurate timing and localisation provided by the on board GPS receiver, an astronomical computation can be effectuated and the Sun azimuth as well as an auxiliary's target azimuth can easily and quickly be determinated. The precise Sun's crossing of the split photocell, amplified by the telescope's magnification allows azimuth' accuracies of a few seconds of arc.