The Palomar Transient Factory Photometric Calibration by Ofek, E, Laher, R, Law, N, Surace, J, Levitan, D, Sesar, B, Horesh, A, Poznanski, D, van Eyken, J, Kulkarni, SR, Nugent, P, Zolkower, J, Walters, R, Sullivan, M, Agueeros, M, Bildsten, L, Bloom, J, Cenko, S, Gal-Yam, A, Grillmair, C, Helou, G, Kasliwal, M, Quimby, R