What Num in Num 0/X when building mean?

Question

When building workshops, and selecting the material to build the workshop from (if thats even, what I am selecting?!), first I was assuming the num 0/X was designating how many pieces of that corresponding material I would require for building from that.

But these numbers heavily vary each time I build something.

my most recent confusion was after I built a Smelter for which it said for chalk 0/13 and a few moments later I wanted to build a second Smelter and it noted 0/99...

Now I am perfectly clueless, what this means.

So what does the designation 0/99 for building a Smelter with chalk here mean?

Answer 1

As IllusiveBrian communicated already in his comment, the X means in fact, how many I have on stock.

And the 0 is a counter, in my first hours of playing, I haven't encountered a construction that required more than 1 resource, but as soon I was building something that required more than 1 piece of a specific material I saw the 0 was increasing and it stated on the top line "You require 3 more of this" and when ever I selected a material the required counter decreased and the 0/X increased to 1/X where X kept being showing the overall available amount of that resource.