极力推荐，pku-taoshu应用数理统计PPT，对于数据处理分析与编写源代码有很大的帮助。-Highly recommended, pku-taoshu application of mathematical statistics PPT, for data processing, analysis and writing the source code is very helpful.

测试结果：450KHZ之前误差很小，450KHz之后误差很大 这跟单片机处理数据的频率上限有关系，能实现1HZ步进。-Design of AT89S52 based on the frequency meter