These are not ADRs, so the ratio is 1:1, although I am unsure about any "verifiable" relationship between PRCTF and PURE.L (the website and all corporate information only makes reference to the London shares "PURE").
PURE in London (AIM) is currently trading at GBX522 (Pence, or 1/100th of a Pound), or GBP5.22, which is about $7.90 today.
They are also traded in Germany under the symbol 4PC, in Euros. (again, unsure about the verifiable connection to PURE.L).
Liquidity is misable for PRCTF, and the price can be as much as 20% off the London shares (not in the buyer/seller's favor I suppose). German volume is also not great, but in London up to 500k shares are traded in a normal day lately.
Hope that helps.
