Hi Benny, hope you’re having a great time in the spring festival!

I have a question. What does 椅子原来由主椅 means in the following sentence?

另外，性文化节开幕前就被媒体热炒的合欢椅，也成为人气最旺的产品之一。展位摆放了古典型、大班型、休闲型三种类型产品，此种合欢椅乍一看像是一台按摩椅，拉开多种机关记者才发现，椅子原来由主椅、副椅两部分组成，副椅靠背可收折，旋转的椅面可调整高低，扶手可伸延收叠。

Also what does 副椅 is referring to? Are there two chairs, one, the main chair called 主椅 and the other one attached with 主椅 known as 副椅? This is a bit confusing, help!

Thanks!