Usual plate gear have big diameter, but thin in depth, and have a axle hole in the center, so it can be simplified into a thin disc ring.
由于常用的盘形齿轮直径大，厚度小，且中间有较大的安装轴孔，所以可以将其简化为薄环盘，与变幅杆组成变幅器。
"There is no unified flat Earth model, " Shenton suggests, "but the most commonly accepted one is that it's more or less a disc, with a ring of something to hold in the water.
“尽管平坦地球论还没有公认的模型，”珊顿说，”但为多数人接受的观点认为，地球形状是个圆盘，并且在水中托着一圈某种东西。
An annular eclipse occurs when the moon does not cover the entire disc of the sun so that a ring of light encircles the shadow of the moon.
当月亮不能完全遮住太阳时，月亮影子的周围就会有一圈亮光，日环食就发生了。
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