Shipman, N.C. Ben-Zvi, I. Burt, G. Castilla, A. Hernández-Chahín, K.G. Macpherson, A. Mitchell, J.A. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-TUPB014 English 415-419 TUPB014 cavity ion niobium luminosity cryomodule Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-TUPB014 http://jacow.org/srf2017/papers/tupb014.pdf A four wire measurement was used to measure the bulk RRR on two DQW Crab Cavities. The measurement procedure is explained and the values obtained for each cavity are compared together with the values obtained from Niobium samples of the same stock from which the cavities were manufactured. Measurement errors and carefully analysed and further improvements to the measurement procedure are suggested.