用一支量程为250克或500克的弹簧秤,在刻度板与四个固定螺钉间加上薄垫圈。然后,在上下两螺钉间系上粗棉线(或用几股细线拧成一股),也可用细橡皮筋。线要绷紧,使之不能与刻度板接触。将罐头盒铁皮剪成宽为3毫米左右的长条,其长度以两端卷成小圆筒刚好能套在两边的线上为准,如图所示。小圆筒不能将线套得太紧,以由线的摩擦而铁片不会下坠,稍受推力 Use a spring scale with a span of 250 g or 500 g and a thin washer between the scale plate and the four set screws. Then, between the upper and lower screws, thread a coarse cotton thread (or use a few strands of thread to twist into a strand), or use a thin rubber band. The line should be tight so that it cannot come into contact with the scale plate. Tin cans were cut into strips with a width of about 3 mm. The length of the tin can be rolled into a small cylinder at both ends and it fits the line on both sides. The small cylinder can not put the thread too tightly, so that the iron will not fall due to the friction of the wire, slightly pushed by the thrust