I have seen an example referring to "on a par with something" at Cambridge Dictionary:

"At this rate, they'll have 600,000 visitors to the exhibition, which will put it on a par with the Van Gogh exhibition."

However, I'm not unclear about the overall meaning of the sentence. What confuses me here is how the word "which" is used. I don't understand which noun 'which' complements for here. Surely, it cannot provide information for "the exhibition" because of its improper meaning.

So, what does "which" complement for in this case?

Also, can "which" complement for the whole preceding clause? I'm very doubtful about this, because if I comprehend this meaning in this way, it seems to be quite proper.