Please notice first the relay and its according contacts in front. The finger-pair, being activated by the relay designated '18'. Please notice the left-hand side taller switching-fingers. The most left-hand side one is wire-wound by some resistance wire; which is heating up the bi-metallic left-hand side finger. In front you see the two sets of switching relay contacts. The bi-metallic fingers are moving, when a certain temperature has reached, to the right-hand side. The adjustable resistor in front is to adjust the switching-on time-delay. Rö 1 designated black tube is the housing of the 220 V mains supply neon-indicator. Please view carefully the slowly responding bi-metallic finger towards the right-hand side. The sound of a buzzer is indicating the instant the circuitry being activated.