A method of monitoring a condition of a connection between two bodies which are connected using a connector. The connector has a sensor assembly which provides an output representing a degree of movement of one or both of the two bodies. The method includes installing the connector and the two bodies in a use position in which the connector joins the two bodies, and using the output from the sensor assembly and a numerical model to determine a force on one or both of the two bodies or of the condition of the connector. The numerical model is a record of test forces applied to a test element secured to the connector or of a test connector having a same configuration as the connector and a corresponding output from the sensor assembly of the connector or of the test connector during and/or after the application of each test force.