Unlike the Optonica, this is not a self-contained system but an add-on unit intended for use with an existing stereo system.

A number of add-on units are available for the Spectrum which, almost without exception, use the allophone method of synthesis.

An electronic map display could be a single add-on unit, or part of a sophisticated electronic system already available on luxury cars in Europe and Japan.

PCT application 82/03520 explains how an automatic shutoff unit can either be built into a domestic appliance or installed as an add-on unit to existing equipment.

An optional add-on unit extends the radars coastal defense capabilities.

In principle, the equalizer is an elaborate set of tone controls contained in an add-on unit that plugs into the amplifier or receiver.

Meanwhile, integrated dealer-installed radios for either service typically cost $325, and after-market add-on units can be purchased for $200 or more, including installation.

They are not typical as CIP systems in industrial use tend to be complete add-on units.

The amplifier power can affect your overall enjoyment, and add-on units have more power than most factory-installed systems, but the amount varies.

While they did work technologically, forcing compatibility involved modifying the add-on units' shapes or using 3rd party expanders.