HD Clone Pro: Identifying Identical Drives

I've been using HD Clone Professional for several weeks and it works great most of the time.
Question: The original drive is a 160 GB WD MY PASSPORT. I want to clone it to another 160 GB MY PASSPORT drive.
When I boot from a CD (which I've found to be more stable), how can I tell which drive is the original/Source and which is the blank/Target drive? They appear identical and I don't want to wipe the original drive.
Please advise.
- John
Question: The original drive is a 160 GB WD MY PASSPORT. I want to clone it to another 160 GB MY PASSPORT drive.
When I boot from a CD (which I've found to be more stable), how can I tell which drive is the original/Source and which is the blank/Target drive? They appear identical and I don't want to wipe the original drive.
Please advise.
- John