Human hearing is approximately logarithmic with respect to the perception of both level and frequency. Logarithmic increments mean that there is a constant ratio between the individual steps on the scale. In the calculation of dB, the base 10 logarithm is used. The base 10 logarithm of a number is that number to which 10 must be raised, to give the number itself. Power is measured in watts, so this transformation will apply to everything that can be measured in watts, in the form of acoustic as well as electrical power (this transformation will thus not apply to amplitude values such as sound pressure, current, or voltage). In acoustics and electronics, specific reference values are applied as a basis for the specified ratio in dB. Instead of specifying the reference in full, in some situations one or more letters can be appended after the “dB” to indicate the reference.