[simon.a.billington]

Analogue devices are just maths in physical form. That's hoe circuits are designed. Every component or series of components are designed to do something "mathematical" to a signal, whether it by as simple as "summing" or a more complex "algorithm"

It may not work with digital values, but it does works with voltages and amps instead, but its the same principle. Which is why its possible to make "emulations"