If you are investing and trading in altcoins, rather than simply purchasing Bitcoin, this is a must see video. It clearly and succinctly explains why you need to be measuring your gains and losses against BTC value, rather than USD (or other fiat currency).
Please take the time to watch this, so you can more accurately determine if you are gaining value within your portfolio, or if you are inadvertently destroying value.
“Bitcoin and altcoin investors tend to measure their cryptocurrency gains in US dollar terms. While this is fine to do with Bitcoin, your altcoin investments should always be measured against Bitcoin to determine whether or not you generated value for yourself.
If you aren’t keeping track of how your performance would have been had you just bought Bitcoin rather than your current investments, you are measuring your performance incorrectly and may be destroying more value than you know despite the fact your portfolio has doubled in US dollar terms!”
You may watch this directly in Youtube, to see more comments (and some great links) from the video creator. It is worth subscribing to his Youtube channel.