ATR Calculation

[Beauregard]

Hi

Somehow I am stuck with understanding how the ATR is calculated. I understand the formula and the code, but somehow I get different results.
I have this data: (Date, Open, High, Low, Close)
15.10.2012 1428.75 1441.31 1427.24 1440.13 16.10.2012 1440.31 1455.51 1440.31 1454.92 17.10.2012 1454.22 1462.2 1453.35 1460.91 18.10.2012 1460.94 1464.02 1452.63 1457.34
When I calculate ATR(1) with NT I get these values:
15.10.2012: 14.07
16.10.2012: 15.38
17.10.2012: 8.85
18.10.2012: 11.39
They are correct.
When I calcluate ATR(2) with NT I get these values:
17.10.2012: 11.57
18.10.2012: 11.48

To my understanding this should be the average of 2 ATR. But it is not. The average would be 12.12 and 10.12

thanks for your feedback
Do I overlook something

[NinjaTrader_Joydeep]

Hello Beauregard,
The SMA is calculated as the (current value + last average value)/2. You can calculating it as current value + previous value)/2.

[Beauregard]

Hello Beauregard,
The SMA is calculated as the (current value + last average value)/2. You can calculating it as current value + previous value)/2.

Edited 17.11:
Ok, I see what was misleading to me. The definition in the help section it is written that ATR is a moving average, which I assumed to be a simple moving average. In fact it is an exponential one