A comparison of the ozone primary reference standard photometer serial number 45 (SRP45) against the National Institute of Standards and Technology (NIST) instruments, serial number 0 (SRP0) and 2 (SRP2), has been performed in order to establish the traceability and comparability of ozone measurements made by the Chilean atmospheric science community. A complete uncertainty budget was developed for SRP45, using a GUM approach. The results of the comparisons allow us to conclude that SRP45. SRP0 and SRP2 are comparable according to internationals criteria over an ozone mole fraction range of 0 nmol mol(-1) to at least 500 nmol mol(-1). The official result for the validation of SRP45 is x(ozone)(SRP45) = [0.013 + 0.99806x(ozone)(SRP2)] nmol mol(-1) with an expanded uncertainty of 2 x root(0.27)(2) + (1.18 x 10(-2) x x(ozone))(2) from 0 to 500 nmol mol(-1). (C) 2011 Elsevier B.V. All rights reserved.