Abstract: A pair of members which are expandable and contractible with temperature have a flexible expansion joint therebetween. A first body is attached to one of the members and carries an elongated support having a pair of indicators slidably mounted thereon. The indicators frictionally engage the support so that they move only in response to movement of the spaced members. A second body is attached to the other of the members and has a slot therein through which the support freely extends. The indicators have an outer dimension greater than the width of the slot. The second body has opposite faces which engage the indicators.