The Post Office has been quietly recruiting customers passing through its transformed Oxford branch for biometric experiments in a bid to better understand the stress points in the customer journey. It has been strapping heart monitors and cameras to consumers as they wander around the store, noting the points where the body reacts badly to things such as poor signage. It comes as part of a complete overhaul to the way it gathers and uses data from the 17 million customers it serves each week.