DWG files - which version of AutoCAD?

Scenario:
You have been sent a dwg to work on and must send it back in the same format it was received, but you do not know which version of AutoCAD it was last saved in.

Solution:
- Right-click on the DWG and Open With Notepad
- Read the first 6 characters and match them to the following versions:

AC1027 - AutoCAD 2013, 2014, 2015
AC1024 - AutoCAD 2010, 2011, 2012
AC1021 - AutoCAD 2007, 2008, 2009
AC1018 - AutoCAD 2004, 2005, 2006
AC1015 - AutoCAD 2000, 2001, 2002
AC1014 - AutoCAD Release 14
AC1013 - AutoCAD Release 13
AC1009 - AutoCAD Release 11, 12
AC1006 - AutoCAD Release 10
AC1004 - AutoCAD Release 9
AC1003 - AutoCAD 2.6
AC1002 - AutoCAD 2.5

You can now save back to the nearest format.

SC