FWIW, the universal convention in FX markets is to quote in terms of UNDerlying currency/ACCounting currency (sometimes also called BASE ccy/QUOTE ccy), ie the price of one unit of the underlying ccy in terms of accounting ccy.
Thus, the generally quoted price is BTC/USD (around 5000 as of this time), namely the price of a Bitcoin in USD. USD/BTC, on the other hand, is the price of one USD in BTC, or about 0.0002. (Of course it might well be the other way around in a year or so.)
Note that CC1/CC2 * CC2/CC3 = CC1/CC3, and thus
CC1/CC2 / CC3/CC2 = CC1/CC3,
which is where that odd convention originates from (because setting eg CC2=USD, you divide the dollar price of CC1 by the dollar price of CC3 to get CC1/CC3).
Thus, the generally quoted price is BTC/USD (around 5000 as of this time), namely the price of a Bitcoin in USD. USD/BTC, on the other hand, is the price of one USD in BTC, or about 0.0002. (Of course it might well be the other way around in a year or so.)
Note that CC1/CC2 * CC2/CC3 = CC1/CC3, and thus
CC1/CC2 / CC3/CC2 = CC1/CC3,
which is where that odd convention originates from (because setting eg CC2=USD, you divide the dollar price of CC1 by the dollar price of CC3 to get CC1/CC3).
EDIT: clarify