hey newtrader...... it's not using 14 days/bars......  rsi is one of the indicators that builds on it's previous value.....  and it's previous value was created using  it's previous value which was created using its previous,,,,,,,,   .....  so in a sense,  every bar loaded in the chart is be used to calculate  the current bars rsi(14).....

somewhat like the image you see created in a mirror when  you place 2 equal sized mirrors directly across from each other....   it's the math.....h