That was such a hobbyhorse of the master, to torture his apprentices with questions of knowledge. So suddenly he stood before me: What is a kilocalorie? However, I had just passed my Abitur graduation at a science- oriented gymnasium and had even been orally examined in physics. This is the amount of heat that is needed to heat 1 kg of water from 14.5° C to 15.5° C. The heat is then used to heat 1 kg of water.

Wrong, that is the amount of heat needed to heat 1 kg of water by 1°C. Then the discussion started in which I tried to explain to him that the amount of heat needed to heat 1°C was not always the same. Perhaps you have an idea of how the discussion might have ended?

No, but the resolution is quite simple. At some point the next job came, in this case to clean a black car. I was in the wash hall and worked with the sweat of my face. Anyway, there were no car washes like nowadays in our area yet. Then execution announced. The master inspects, strokes his finger over the inner edge of a fender and notices that there is still dirt. Once more!

As you can see, the education at that time was not only related to automotive technology, but holistic, although the word was probably not yet so well known. Anyway, from now on I discussed with the master occasionally and in quite a different way if happened. In the end my personality did not suffer any noticeable damage by this.

The (kilo) calorie is still there today at best, if you want to lose weight. Otherwise it was equated by 'Joule' with the remaining energy. In a physics book the Celsius scale has no place any more and with it the °C disappears too, no matter if in short form or written out. However, the arbitrarily chosen distance at that time is still to be found in the Kelvin scale. It would probably have been too much upheaval to adapt the more devided one.

The Anglo-Saxon countries use the scale of the German physicist Daniel Fahrenheit, which indicates the melting of water by 32°F and its boiling by 212°F, i.e. multiply from Celsius to Fahrenheit by 9/5 and add 32. And how is the temperature measured? One method would be to take advantage of the volume or length expansion.

So use a pressure rod made of a material whose expansion behaviour under heat is known, place a pointer which shows this relatively small change multiplied. Now, for example, the calibration with melting water and the boiling of the same temperature should be transferred to the rod and the scale between should be supplemented by a hundred equal distances.

Two different non-electric thermometers are used industrially, the gas and the bimetal thermometer. The latter is much cheaper and in the simplest case consists of a coiled strip of two interconnected metals. It is important that these have significantly different thermal expansions (top picture). However, a coil spring made of two such metals can also be installed. The spring thus extends and retracts depending on the temperature and moves a pointer.

With gas thermometers this is done by thermal expansion, e.g. of helium gas. A typical feature of this type of thermometer is the often long capillary, which allows the dial gauge to be placed independently of the measuring location. Up to 40 m are possible. It is faster at the display, but unlike the bimetal thermometer, it may depend on the ambient temperature. In the past such measuring instruments were typical in cars with retrofitted measuring instruments, e.g. for the oil temperature.

Nowadays, of course, they're electric. If one is specified with the device, like e.g. 100 Ohm, then that is the one at 0°C. It does not always have to be an NTC, also sensors are possible, whose resistance rises with the temperature (PTC). Since such thermometers require a power supply anyway, the display can also be digital, e.g. in a car.

Thermocouples are not dependent on current. Two metals arranged very differently in the voltage series are electrically connected to each other and generate a temperature-dependent voltage. This can then be used for display purposes. In general, the temperature range for which a thermometer is designed or calibrated must be observed. Above or below it becomes inaccurate. The thermometer can be used in In exceptional cases they can even be damaged. Calibrated, particularly accurate thermometers are usually only approved for a small temperature range and can also be quite expensive.