Thought I would do a quick walk-through IDing this coin via Helveticas tables as echizento had mentioned them earlier on in the thread. It could help you in the future.
Don't be disappointed by the AORTA book Hatter, its still a very good resource its just that so many ancient coin types exist its unlikely anyone will ever manage to get all variants into one book (I do believe Raz is looking at an ERIC III book with 500,000 types in it though!).
Quick bit of background:Helveticas tables are downloadable Excel spreadsheets with many later Roman coins in them allowing quick IDing of the more common coins.
The spreadsheets are based on the info in books called RIC (Roman Imperial Coinage) produced over the last 100 years offering arguably the most complete 'list' of all Roman coins. Most people quote RIC numbers as a way of identifying their coins. RIC can be difficult to read for beginners and comes in 10 Volumes probably setting you back $1000 so not many people have their own copies. Its also badly in need of a re-write to bring it up to date and improve the 'user interface'. This is where AORTA, ERIC I, ERIC II and in the future ERIC III etc succeed, they are much 'nicer' books to use.
Helvetica is the name of the lady (Dane) who manages them - they are a fantastic free resource though I do believe for a small price you can order the spreadsheets from her on her website.
The last thing you need to know is that you will need Microsoft Office and Excel on your PC to use them.
OK - Using them this is how to ID your coin:Visit the site:
http://www.catbikes.ch/coinstuff/coins-ric.htmScrolling down you see titles on the left and pictures of coins on the right, find your coin reverse, or something similar. In this example we need the very last entry at the bottom of the page called 'VOT.. (V, X, XV, XX etc)'.
Clicking 'VOT.. (V, X, XV, XX etc)' will download the spreadsheet to your machine, then you should open it. Then we need to select the correct sheet by looking at your coin and clicking the correct tab at the bottom of the spreadsheet. Your coin is a VOT XX so click the 'VOT XX' sheet.

Make sure your scrolled fully left and fully up so you can see cell A1 in the top left of screen. Not sure how good you are with Excel but we must now use the filters at the top of each column to narrow down the number of coins visible. Easiest place to start on your coin is with the text inside the wreath on the reverse. Yours says VOT / Dot / XXX / Blank.
At the top of the page in column E click the downward arrow next to 'Line 1' and deselect everything but 'VOT' in the options list and click OK.

Do the same for 'Line 2' column F but select 'Dot' only.
Do the same for 'Line 3' column G but select 'XX' only.
Do the same for 'Line 4' column H but select '(blanks)' only.
You will now see the huge list of coins has been reduced to just 27 by filtering out all coins that do not have the same 'in wreath' text as yours.
From this we can then see only coins of Constantine and Licinius remain, the next best thing to filter by is the reverse mintmark (6pm), we can see yours says 'TSAVI', now filter column J, 'Mintmark (in ex.)' accordingly.
Bingo, we are down to just 3 coins!
The only thing left to filter is the 'Other details where known' column, if you look at your coins reverse at 12 o'clock on the wreath is a star, filter accordingly and we are left with just two coins that cant be separated any further using these sheets, under the RIC column these two coins are described as RIC VII Thessalonica 117 and 123.
Not sure how to separate them further, perhaps it could be done with weight, I would need to look at RIC to see if this can be done but not got time right now, maybe someone else can chip in and take it further or maybe do a 'step-by-step' of anther method of IDing such as Wildwinds.
As you get used to IDing these coins you will build up half a dozen methods and resources of IDing which between them can ID all coins but individually they all omit certain variants.
*Edited to add pics of coins to stop paging back and forth*

