I want to measure the temperature of a metal stage where I am holding a sample. What I have done is to clamp both wires from a thermocouple against the stage using a bolt and washer. Supposedly this is not the best practice but I don't see why this would be a problem. I have read that you are supposed to weld the thermocouple wires together at one end, at the location you wish to probe. What is the purpose of this? It seems to me that as long as the two wires are at the same temperature, and are in electrical contact, the thermocouple will work. Welding the wires will decrease the resistance, but if the other end of the thermocouple is an open circuit for measuring a voltage, there will be no current flow so the resistance will not give rise to any spurious voltage. If there is a temperature difference between the two wires, there may be an additional thermoelectric voltage. But as long as the two wires are close together there should not be a large temperature gradient. In any case, is there some effect I am neglecting here?