inventory level for product variations

I am trying to set inventory levels for product variation.

Example. I got a shirt that is small medium and large.

I have 5 small 2 medium and 10 large.

How do I go about setting the inventory levels for these different variations? Currently I only see one inventory level for the whole product..

Is this even possible?

http://ww.wp.xz.cn/extend/plugins/foxyshop/