DEAP-3600 is a direct detection dark matter experiment using a cryogenic liquid Argon target mass. The detector is situated within a water tank and placed 2 kilometres underground at SNOLAB to shield it from outside sources of radiation. However, contaminants on the inner surface of the spherical acrylic vessel (AV) can trigger the detector and must be removed using data analysis. A cut is applied to remove such events that reconstruct near the surface of the AV, but the efficiency of this cut is strongly dependent on the accuracy of our reconstruction algorithms and so it is vital to understand the resolution of these fitters. This presentation details the development of a data-driven method for measuring the position resolution of a charge-based reconstruction algorithm. In February 2019 the collaboration released a first year paper with 758 tonne-day exposure, in which we showed a resolution of ~20 mm for events near the detector surface.