Argus Light Meter ?

I purchased this item over the weekend and unfortunately I don't see a model # on it.

Can someone please tell me what exactly this item is and whether it's complete or not. The "sail" doesn't make a complete circle.

Thanks !

It is an Argus flashgun, not a meter. The "sail" will make a complete circle if you pull it to the point where the lip hooks in place. It slips into the hotshoe

The reflector ("sail") will make sort of a bowl shape when you pull it and put the tab into the slot.
After that, you'll need some batteries and flashbulbs. For the exposure calculation, you'll need the guide number which depends on the particular bulb you use (generally printed on the box of bulbs).
You'll also need a camera that can sync with flashbulbs. It may be easier to use it as decoration.

Lots of companies made variations of these, and they are pretty common in antique shops and random collections of photographic "stuff".