Recently, my hot water geyser wasn't heating water.. so I called up the electrical guy and he came to repair it. I don't know what he did, since I wasn't home when he repaired it.. my mom said that he 'set' the thermostat at 65 deg. C. How exactly do you 'set' a thermostat? Since it's just a bi-metallic strip, how can u so finely graduate it to such a setting? and it's not just with the geyser.. even home heaters and ACs use similar kind of thermostats. How are they 'set' to certain temperatures?