Explanation on RunPeriod in EnergyPlus

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Hello All,

I am using EnergyPlus v9.0.1 with BCVTB (v1.6). While running the BCVTB Example with IDF file SmOffPSZ.idf I noticed that the simulation starts at 01/01/2017 for RUNPERIOD1 and subsequent one are on 01/21/2017, 02/10/2017, 03/02/2017 ...

In my IDF file I have RunPeriod object as,

And SimulationControl as,

I am using a weather file for STOCKHOLM_ARLANDA, WeatherFile

Now I don't understand why the simulation starts in the year 2017 and also why it jumps 21 days? I tried reading the InputOutput Reference from EnergyPlus, but it was not clear why this is happening.