Apexi rev/ speed meter what does it do???

[TorbayGlanza]

I have one of these in my car and I can't understand any possible good use for it does any one else have one? What does it do and does it do anything cool?

 

[Moonbox]

It delimits car, can also display a heap of cool features if you have the optional g sensor. gives 0-60 times etc. estimated bhp aswel