This is a good question. I know what you're trying to do. The question is how "realistic" do you want this test to be? If you want to do it on the exact same machine with the same instance of Armory, you can do the exact same process, but it will feel like you're cheating. But if you repeat the process with a real online-offline pair, you'll already understand it. You kind of have to do this, because Armory won't let you have two copies of the same wallet at the same time. You're going to have to simulate it.
The way it works is because the watching-only wallet behaves exactly like a regular wallet, except for one critical distinction: it can't sign transactions. You go through the exact same process of entering recipients, and confirming, but only the "Create Unsigned Transaction" button is there, not a "Send" button. So up until the moment you would've hit send, it's identical. For the watching-only wallet, you will create the unsigned transaction to be signed by the full wallet.
However, there is the "Create Unsigned Transaction" button even when you are using a full wallet. So when you create the transaction, you can pretend it's a watching-only wallet and simply click the "Create Unsigned Tx" button instead of the "Send" button. Then you can follow the procedure for completing the transaction. Save the unsigned tx to disk. Then go back to the main menu and pretend that the file you saved was just brought to your offline computer from a USB key. Click "offline transactions", and click "Sign and/or Broadcast Transaction". Load the *.unsigned.tx file, and it will allow you to review the transaction and verify it is what you expected. Click "Sign", and it will not only sign it, it will overwrite the original one with the signed transaction back to disk.
So you can close that window and pretend that you just brought the signed transaction back to the online computer. Click "offline transactions" again, sign and/or broadcast, Load the *.signed.tx file (review it again, if you like), and click broadcast. Now you're done. In a real online-offline split, each file save and load would be via USB key, and you'd move it between the systems as necessary.
Thanks for your answer!
What I am doing in the moment is testing with small BTC-amounts to better understand BTC and applications like Armory before really working with them, endangered to loose by my own silliness greater amounts or -in this case- using a
really different PC for watch-only wallets.
So I startet my trials exactly as kindly described, than tried somehow different methods.
I always could proceed more or less, but in the end I was never successful.
Long story, always any errors (unspecified Win7 Runtime errors, not saving file without any explanation,
Armory (not me!) suddenly forgets my passphrase...(had to restore), Error like: "SelectCoins returned a list of size zero. This is problematic and probably not your fault."... and so on.
Have no idea. Cannot understand that. Should not matter where a file was created.
Perhaps the problem might be, that Armory does not tolerate special writings in its data directories.
So I tried it with subdirs. At first this seemed to work, but then... as before.
