游标卡尺和CPU

在“科创网”的App“科创”注册时弹出游标卡尺，要把副尺拉到正确位置才能获得验证码。

网友订的CPU制作完成 | 计算机电子学 - 科创

Who Invented the Vernier Caliper | 游标卡尺 | 游标卡尺的读数方法 | 游标卡尺的读数原理 | How to Use a Vernier Caliper

主尺每个格子1 mm，十分度游标卡尺10个格子共9 mm，即每个格子0.9 mm。

 

上面右图中，被测物体的长度为l。l = 7 + x

7 + x + 5 * 0.9 = 12

解得x = 0.5，所以l = 7.5 mm。改写上式，把x和小数部分放左边，整数放右边：

7 + x + 5 * (1 - 0.1) = 12

x - 5 * 0.1 = 12 - 7 - 5 // 几个整数算完了还是整数，出不来零点几。

再如，当游标上刻度为9的线与主尺上某根线对齐时，不用去看主尺上该线的读数，必有：

x - 9 * 0.1 = 0 // 右边算完必为0。为了使等式成立，左边必须把零点几消掉。

所以x = 0.9。比如l = 13.9，主尺上该线的读数 = 13 + 0.9 + 9 * 0.9 = 22。9 * 0.9是8.1不是0.81，害我迷茫了半天。:-)

x - k * 0.1 = 0  // x = k * 0.1

游标卡尺的英文是Vernier caliper。Vernier是人名。caliper也可拼做calliper(两个个l).

caliber (n.)
"inside diameter of a gun barrel [枪管]," 1580s, from French calibre (by mid-16c., perhaps late 15c.), often said to be ultimately from Arabic qalib "a mold for casting." Barnhart remarks that Spanish calibre, Italian calibro "appear too late to act as intermediate forms" between the Arabic word and the French.

枪管内径和铅弹直径不准，就漏气打不远。

1992年5月，在扬州市邗hán江区甘泉镇的一座东汉早期的砖室墓中出土了一把铜卡尺。它的出土纠正了世人过去以为游标卡尺是欧美发明的错误观念。The idea of the caliper being used as a tool for measurement has been dated to at least 9 AD during the Xin [王莽的新] Dynasty.