For example, on a 15min bar (bar A) right after the close of bar A I read the 200 SMA and 200 EMA at 45.90 and 45.99 respectively. Then a few hours later I go back to that exact same bar (bar A), but the SMA and EMA have changed and are no longer the 45.09 and 45.99. I do not understand why this is. I thought once the value was calculated for the 200 EMA and 200 SMA at that specific time point, that would always be the value at that specific time point. Then as time went on more calculations would be made to continue the curve of the EMA and SMA, but the value for the SMA and EMA on bar A would remain constant.
Is there something wrong with my charts (IB)? Or, am I missing something? I get that the most distant value is dropped out of the calculation as another time interval is added to the moving average, but I do not see how this would affect the value of the SMA and EMA on bar A. This makes it hard to back test a strategy by just scrolling through the chart since the EMA and SMA are a different value when compared to the value when they were first calculated.
IB= interactive broker EMA= exponential moving average SMA= simple moving average