An improved control net for Mercury has been completed by utilizing images acquired during the three Mariner 10 flybys in 1974--1975. Relative positional errors within the net are ~1 km on average, and absolute locations are estimated to be better than 25 km. The analytical triangulation resulted in new values for focal lengths (Camera A: 1493.6 mm; Camera B: 1500.1 mm), W0 (329.548¿), and camera orientation angles for 811 images acquired during all three flybys of Mercury. ¿ 1999 American Geophysical Union