Fig. 4: On-body test of the watch.

a Photograph of a volunteer wearing the watch with blood glucose levels displayed in real time. b Workflow of the glucose-monitoring watch. c The blood glucose variation curve of a volunteer measured by the watch during the daytime compared to true blood glucose values (reference) obtained from finger blood. d Glucose concentrations before and after a meal measured by the watch from five volunteers. Data represent the mean ± s.d. of five replicates. ***p < 0.001 by Student’s t-test. e Plot of glucose concentrations measured from 23 volunteers by the watch and by a commercial glucose meter