A set 'day rate' — Most providers take the mid-market rate, and apply a margin on top, without being transparent. So you have no idea how much they're over charging you by. An unfair deal on your currency — By hiding the real charge in the exchange rate offered, most providers make huge profits at your expense, and you're none the wiser. Jan 15, 2021 · They support stocks, foreign exchange and crypto historical data, technical indicators, and sector performance. Twelve Data. Twelve Data was founded in 2009 and is getting more traction lately. The main features of the services they provide include: Real-time and historical data via API; Plotting dynamic charts; Large technical indicators list Monthly averages The monthly average endpoint returns monthly average rates for a single base currency and one or more counter currency for the year you specify in your API query. Currency volatility Volatility measures the fluctuation in the exchange rate of a currency pair over a specific period, represented in a percentage.