Help with radio code

[Mitch H]

I had a standard unit in my car rcd300 if I remember rightly?
I have had a brand new vw rcd510 fitted about a month ago.
Since had some work done on the car (gearbox oil cooler) so they've had the battery off and it's now asking me for a code.
Is the code unique to the car or the unit itself?
And where can I retrieve it. Probs been asked many times before but was unsure with me changing the stereo.

[Mitch H]

Doesn't matter   
Just messaged the chap who fitted it and said it's written on top of the unit so just a case if taking it out if I remember how he got it out lol
I've had a cherry red hazard switch to fit for ages so will finally get it fitted