Recent development in self-monitoring devices indicates that using quantified data in clinical practicesupporting chronic diseases management holds a big potential. However, exploration of this design space also suggests that some unattended challenges still exist, such as a low adoption rate of self-monitoring tools in existing clinical practice. In this text, wetherefore focus on the ways healthcare professionalsuse quantified data in their practice. We draw onempirical data from an ethnographic study of a cancer rehabilitation center. Our preliminary findings suggestthat the self-monitoring tool supported the nurses'work because it became a functional complement totheir work by allowing them to appropriate the deviceto their and the patients' needs.