lol I tried send you some sats to pay them with

the only reason you can make the conversion BTC->XMR 
or to whatever

is because you have an underlying UoA denomination to compare them with.

its the US dollar.
it denominates everything.

you are comparing
two USD denominated prices.

the price of one thing.
as measured in USD.
against.
the price of another thing.
as measured in USD.

fiat graph.