1. A system for monitoring a validator that assesses a payment token, the system including: an input device configured to receive messages from a machine including a validator, the messages containing data indicative of validator events; and a processor configured to: derive timing information for the validator events from the messages; maintain a record of validator events and associated timing information for those events; assess relationships between sets of two or more events to determine whether predefined criteria is met for any of those sets of two or more events; and perform a specified action in the case that at least one of the predefined criteria is met.