根据游标原理，说明1／20mm和1／50mm卡尺在读数上的区别

视频讲解 游标卡尺读数方法
10格 http://v.youku.com/v_show/id_XODA2MDc4OTE2.html?from=y1.7-1.2
20格 http://v.youku.com/v_show/id_XODA2MDk0NzM2.html?from=y1.7-1.2
50格 http://v.youku.com/v_show/id_XODA2MjA3MjY4.html?from=y1.7-1.2
螺旋测微器测微器 http://v.youku.com/v_show/id_XMTI1MzA1MTUyMA==.html?from=y1.7-1.2

安培分子电流 视频讲解
http://v.youku.com/v_show/id_XNzQ5ODEyMTgw.html?from=y1.7-1.2