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system
why the currency data(such as usd/jpy) is different from different source
user
a day is a long time and the rate is not the same all day. some sources will report a close price that averages the bid and ask. some sources will report a volume-weighted average. some will report the last transaction price. some will report a time-weighted average. some will average the highest and lowest prices for the interval. different marketplaces will also have slightly different prices because different traders are present at each marketplace. usually, the documentation will explain what method they use and you can choose the source whose method makes the most sense for your application.
assistant