The scale of the room thermometer given in the example is broken in degrees Celsius (only why the scale is located horizontally?), and from the list of temperatures the closest to the temperature that reflected on this scale two values are suitable:
2) 18 ° C
4) 291 ° to
Now it is quite fashionable (just not clear for what) to produce indoor thermometers with two scales. From one side it is gathered in ° C, from the other ° F. Only in this case, the graduation (intervals between the marks) in these scales are different and does not coincide. In the shown picture, although there is no inscription denoting units of measurement, with a high degree of probability it can be assumed that these are degrees Celsius. Therefore, 18 ° C is displayed on the thermometer because there are only five intervals between the marks of tens of dozens and their price is 2 °. But if you look more accurately, then about 18.2 ° C.
The price of division of this device = two degrees, based on this, the readings of the thermometer are equal to the standard eighteen degrees, it is not hot, of course, with a naked belly and in swimming trunks you do not take a walk, for this, you need to raise it by three to four degrees, you will have to be content with the fact that the indoor device shows.