What does the Denomination search filter do?

I expected it to limit the results to items with the specified denomination, but it doesn't do that.

(The help doesn't answer the question. The pop-up help just says to select a currency and the full help page doesn't even include the word “denomination”.)

https://en.numista.com/catalogue/index.php?e=royaume-uni&r=&st=147&cat=y&im1=&im2=&ru=&ie=&ca=3&no=&v=&cu=222&dn=14423&a=&dg=1861&i=&b=&m=&f=&t=&t2=&w=&mt=&u=&g=&c=&wi=&sw=

There are problems with this filter. See https://en.numista.com/forum/topic62094.html#p1312922