Interesting post. One detail I don’t see is how the ROE info actually tells you what currency to convert to. I see the exchange rate calculation but how do you know what the final units are?

I suspect it's this part:

"This ticket was priced in GBP, not INR. Because the journey originated in Manchester, the fare is denominated in the currency of the origin country: the United Kingdom."

So: the currency is the one for the country of origin.