The value of analogue computation is limited. They are not universal computers. The problem with analogue computers is that there's a limit on the number of consecutive operations that they can perform to produce a useful result. With digital computers, errors can be corrected after each operation. Whereas with an analogue computer, evey step introduces noise which cannot be corrected. It cannot be corrected because in an analogue system any input value is 'valid'. In a digital system input values that are slightly higher or slightly lower than a digit can be corrected to the nearest digit.