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First of all, whilst these online portfolio trackers may seem appealing, one needs to take into account that it is sensitive information that you are volunteering to a third-party platform to look after for you, and sometimes, well, they do get hacked into and create a potential mess. See 2021’s
Coinmarketcap’s case for example, where it is believed that 3,1 M emails were leaked, though apparently no passwords nor portfolio data were. Of course, it could just go and happen next time with a more sensitive dataset on whatever tracker (another
recent case apparently has a similar outcome).
Having said that, at least the website seems to be doing things properly (I’m not really a user of the site though). If I create a test portfolio, add a coin, add a buy TX, and then add a subsequent sell TX, the portfolio balance is showing as total balance that equals the current counter value of the remaining assets (bought-sold amount of coin x converted to USD).