answer:I’ve seen one. I wanted to see how the value of euros relative to American dollars had changed since I bought some. I found it by some persistent Googling: as I got warmer, I picked up key terms and used them to further my search. I’m pretty sure that it had a variety of currencies to choose from on both sides of the conversion. I’m not going to sit down now and try to recreate that process, which took a while, but I can at least tell you that I did it and therefore that it can be done.