The characteristic curve of a measuring instrument is the graphical representation of the relation between the physical value being measured, e.g. pressure, and the resulting electrical value. Ideally, the characteristic curve would be linear. The characteristic curve deviation, usually specified at room temperature, indicates the precision of a measuring instrument. Small characteristic curve deviation implies high precision of the instrument. When measuring pressure, thermal drift must also be accounted for in addition to the characteristic curve deviation. It is caused by changes in the temperature of the medium.