首先，解释一下这三个概念

行频(Horizontal Scanning Frequency): 又称为“水平扫描频率”，是指每秒在屏幕上从左到右扫描的行数，单位是kHz；如果行频为110kHz，表示每秒扫描110000行。

场频(Vertical Scanning Frequency): 又称为“垂直扫描频率”，是指每秒钟屏幕刷新的次数，单位是Hz；CRT时代，电子是从左到右，送上到下逐行扫描的，所以，扫描完一列就相当于扫描完整个屏幕，即刷新整个屏幕，故又称为“刷新率”，沿用至今。

显示器垂直分辨率: 显示器垂直方向上可显示的像素数目

显示器水平分辨率: 显示器水平方向上可显示的像素数目

这就很好理解公式了:

　　行频 = 场频 * 垂直分辨率 * K(一个常数)

　　即“每秒扫描的行数”等于“每秒刷新的次数”乘以“每次刷新扫描的行数”再乘以“一个性能常数”

那么，为什么会有一个常数？答案也很简单，由于每次扫描到最后一个像素后，下次又要重定位到左上角，存在一个性能上的消耗，所以“行频”会比“场频*垂直分辨率”大，即K一般大于1。

摘要：

Factors in determining refresh rates

A refresh rate is dependent upon a monitor's horizontal scanning frequency and the number of horizontal lines displayed.The horizontal scanning frequency is the number of times the electron beam sweeps one line and returns to the beginning of the next in one second. Horizontal scanning frequency is measured in kilohertz (kHz).

 A monitor with a horizontal scanning frequency of 110 kHz means 110,000 lines are scanned per second. The number of horizontal lines on the screen depends upon the monitor's resolution. If a monitor is set to a resolution of 1024 x 768 then there are 768 horizontal lines (1024 is the number of pixels on one line).

For a monitor set to a 1280 x 1024 resolution, there are 1024 horizontal lines. Additionally, the time it takes for the electron beam to return to the top of the screen and begin scanning again must be taken into account. This is roughly 5% of the time it takes to scan the entire screen. Therefore, the total is multiplied by 0.95 to calculate the maximum refresh rate.

vertical scan frequency called "refresh rate," it is the number of times an entire CRT screen wasrefreshed, or redrawn, per second. Measured in Hertz, display systems typically ranged from 56 Hz to over 100, but at least70 was recommended to help prevent eyestrain.
The earliest CRTs were unable to support both the highest resolution along with a high refresh rate; however, later CRTsprovided adequate rates at all resolutions. Vertical scan frequency is not an issue with LCD displays because they do notuse phosphors that have to be continuously energized. However, the data from the frame buffer is continuously sent to theLCD panel in order to display animation and video. Thus, the flat panel does have a maximum refresh rate to support motion,but not to refresh static images.

参考：

　　How are refresh rates calculated? And What is the Importance of Refresh Rates

　　vertical scan frequency