different values for same ema indicator

[easyfying]

i am having following problem
every time i change the number of days to load in data series,i get different values for my ema indicator.
like if my dataseries has 250 days,then 200 day ema for fdax is 6466
if my dataseries has 400 days,then 200 day ema for fdax is 6402
if my dataseries has 500 days,then 200 day ema for fdax is 6385
so,how to decide which value is correct and what is the right dataseries length.
in my ema indicator ,i have the maximum number of bars to look back set at default 256.
would somebody look at this issue please.
thank you.

[NinjaTrader_RyanM1]

Hello easyfying,

This is how the EMA is calculated. It uses its prior values in its calculations. More bars will mean it starts out at different prices and this changes the values for the future.

You may prefer using Simple Moving Average if you don't want prior values to affect the most recent 200 bar calculation.