Slots with round end and slots with square end plate screens 长圆孔和长方孔筛板
2.
Slot mesh screen 长方孔筛
3.
4 . make a rectangular hole on any side of the box to observe the projection of the sun . the hole should be big enough to see the whole screen 四在盒子其中一个侧面，开一个长方孔，作观测太阳投影之用，开口不用太大，以清楚看见底部屏幕为合。
