Rooster did a great article on how to read a compass... http://www.roostersailing.com/merchant2/merchant.mvc?Screen=comp&Store_Code=1
I have the Silva 103 compass too, Its the one with 0-19, and the full 360 degree ticks. I put an up arrow and a down arrow on the sides of the compass, and that helps me quickly decide if Im getting headed or lifted, pretty much if the number gets bigger on one tack, its a lift, and if it gets smaller on the same tack, its a header. Depending on the tack... I probably made this really confusing! Sorry, but hope this helps!
IMHO, the double row model is a marketing gimmick.. The other row is supposed to be your opposite tack heading.. But AFAIK, the rows are fixed together, so you can not change the tacking angle, which does change in lt/med/hvy conditions. Also I question the usefulness of knowing your opposite tack heading in the first place w/o having the means to easily sight other boats/marks (when carrying a hockey pock compass comes into play)
On a single row (0-20) compass if you are on a 12 on one tack, you should be on a 2 on the other tack if your boat's performance matches the compass design.
I thought the point of the double row was that if you were sailing a 12 on the green row on starboard, when you tack you should be on a 12 on the red row on port.
The advantage is that increasing is always a lift (might be the other way around), where as for a single row compass it is opposite for either tack, as explained by ChalmersP above.