How can I use an existing Time Machine backup with my new computer? I've just replaced my existing MacBook Pro with a new MacBook Air.  I've got 18 months of Time Machine backups from the old computer.  I'd like to configure my new computer to use the old computer's Time Machine backups, so the new computer picks up where the old one left off.  Is this possible?  If so, how?

I didn't restore the new computer from a Time Machine backup because my old computer used more disk space than my new computer.  There was a lot of cruft as well, so I decided to start from scratch on the new one.  I'm slowly pulling off individual files and settings from a clone of the old computer's hard drive.
I found the following solution here:

sudo tmutil associatedisk -a "/Volumes/Macintosh HD" "/Volumes/Time Machine Disk/Backups.backupdb/John Doe's MacBook/Latest/Macintosh HD"