How can I see which Delphi version a .dcu was compiled with?

If I have some .dcu files; how can I find out which Delphi version they were compiled with?

I received some old source code, and some .dcu files are included, and I don't have access to the original source code. I want to refactor this library out, but for that I want to just make it compile in the original Delphi version first.

_{By the way, the compiler could be a bit more helpful here.
It states that file X was compiled with a "different" version, without saying -which- version that is....}

Solution

From unofficial sources, look at 4th byte of the .dcu

$0F = Delphi 7
$11 = Delphi 2005
$12 = Delphi 2006 or 2007
$14 = Delphi 2009
$15 = Delphi 2010
$16 = Delphi XE
$17 = Delphi XE2
$18 = Delphi XE3
$19 = Delphi XE4
$1A = Delphi XE5
$1B = Delphi XE6
$1C = Delphi XE7
$1D = Delphi XE8
$1E = Delphi 10 Seattle
$1F = Delphi 10.1 Berlin
$20 = Delphi 10.2
$21 = Delphi 10.3
$22 = Delphi 10.4
$23 = Delphi 11

There was no change in .dcu format going from Delphi 2006 to Delphi 2007. Therefore they use the same.

Edit Jul 2, 2016 Added XE8, 10 and 10.1 to the list.

On request, also the target platform, which is found in the second byte of the .dcu. Values are of course valid only for versions that have these targets.

$03 = Win32
$23 = Win64
$04 = Osx32
$14 = iOS emulator
$76 = iOS device
$77 = Android

Let me know if you think there's an error.