Summer design weather data

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Hello, I wanted to input the summer design weather data in DesignBuilder when I realized there are two ways to do this. the first way is to enter the maximum dry bulb temperature and the coincident wet bulb temperature and the second is quite the opposite. I mean we enter the wet bulb temperature and the coincident dry bulb. As far as I know, we often use the dry bulb and the coincident wet bulb but when do we use the second method? I would be grateful if you could help me with this.