The difference in elevation between two ground points was measured by each of the three field parties using different kinds of leveling instruments. The results are as follows: 1st Party, DE = 18.45 m ± 0.05 m; 2nd Party, DE=18.40 m ± 0.04 m; 3rd Party, DE = 18.48 m ± 0.05m. Determine the most probable difference in elevation between the two ground points.