I bought one of these some years ago for around £35 IIRC
http://www.ebay.co.uk/itm/60cm-Digi...UK_Measuring_Tools_Levels&hash=item35b5b942ad
It's been handy as the 60cm is large enough for any alloy wheel and the laser allows me to do a type of 4 wheel alignment with the toe plates.
I had been using Stu's 6" inclinometer elastic banded to an adapter plate with a couple of screws through to touch the rim for a few years before that. I've seen an inclinometer for £23 that could be extended to fit the wheel and would work the same.
Both have been perfect and accurate enough to 0.1deg. More than you practically need.
So simple to use. Stick it on read the reading. Adjust.
If you need to adjust the camber off the ground. Note down how much you need to adjust by. Raise the car, re-measure the camber and take the adjustment off your new measurement. Drop car, re-measure and be amazed at how close the actual is to the target.
Word of caution, your front toe and camber are directly linked. Ideally learn how to do them both. You can make some toe plates for about £10.
Good luck,
Jim