I will teach you how to make an elliptical gauge.
Take a piece of wood, drill an eye every 2 cm with an electric drill, find two nails that can be inserted into the eye, not too loose, then find a string to tie a knot, and put the string on the nail to draw an ellipse. The distance between the nails and the length of the rope determine the oblateness of the ellipse. Is it okay?
And a triangle.
Find three pieces of wood 3 cm wide and 30-50 cm long, connect them according to a right triangle (if they are not available, use a shooting gun or glue), paint them with white paint, and then mark them with a ruler. All right! ! An isosceles right triangle is easier to make. You can measure the angle with your own triangle.
I don't do compasses or abacus, and I don't think it's necessary for the seventh grade. What a waste!
PS: You can continue to add if you have any questions.
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1. First prepare three boards, 3 cm wide and 5 mm thick. The length is up to you. If you want to be bigger, it will be longer.
2. First, use two plates with the same length as the waist, and the joint of the two plates is sawed into a 45-degree oblique angle, and then the joint becomes a 90-degree vertex angle.
3. Connect the two ends of the other board to the lower ends of the two waists, and it will be OK. Agreed 3 1|
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