The RT Engineering link provided above will provide your answers. Here's the Cliff Notes:
a. If you're dexterous, you can get the clock out without pulling the cluster.
b. This replaces the "guts" of your clock, while retaining the face. You can do it yourself, or have them do it for a fee. The resulting second-hand movement will be smooth, instead of one-second
ticks. This matters not to most people, but purists can tell at a glance a clock that has been retrofitted.
c. The power comes from your car's 12 volt system. No battery connection = the clock's right twice a day.
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