The existence of different calculative cultures, based on the evidence presented here, is detectable in the attitude of senior risk officers to the outputs of risk management models in use. Apparently, senior risk officers develop personal philosophies about the ‘manageability’ of risks by quantitative models. While there appears to be much consensus on the manageability of certain risks (eg, market risks), the issue of non-quantifiable risks and that of internal capital allocation are contestable. BWT’s senior risk officers who had doubts about the use of quantitative models in these contested locales chose to define their area of competence broadly (encompassing risks outside the quantifiable risk framework). Conversely, senior risk officers at Fraser who had more confidence in the reliability of the risk models were able to make them work in the contested locale of capital allocations and performance measurement. However, by doing so, they confined their area of influence to that of measurable risks. This underlines the role of managerial discretion (at least in part) in the selection and use of ERM systems.