Your base currency, is the currency you have, when all your positions are closed. This
should be the U.S. dollar. Let me explain. If all positions are closed you expect the market to go down. If the market goes down, you can buy more bitcoins with the same amount of U.S. dollars, for the next position. So, if youre trading any crypto currency part with BTC as the base currency (like XMR/BTC, ZEC/BTC etc.), you should close all your position when the BTC/USD is in a down trend, since any other coin that has BTC as the base currency will go down too. Lets look at some examples.
http://i.imgur.com/WUYUD5r.jpg(BTC/USDT daily charts)
http://i.imgur.com/6r1Wv5O.jpg(XRP/USDT daily charts)
http://i.imgur.com/tNeWyBS.jpg(ETH/USDT daily charts)
If you study all pairs, you will find out the all BTC base currency pairs are moving in the same direction as the BTC/USD.
Thats why
I only trade crypto currency pairs with the U.S. dollar as the base currency. Poloniex offers 11 pairs I can trade on: BTC/USD, ETH/USD, ETC/USD, LTC/USD, XRP/USD, ZEC/USD, DASH/USD, STR/USD, NXT/USD, XMR/USD and REP/USD. So,
I spread my investment over those 11 positions.