Even taken at around 800 frames per second, its hard to photograph the scanning line on a cathode ray tube (CRT) television. The analogue PAL system runs at 625 lines, with 25 frames per second. Each frame is made up of two interlaced odd and even "fields". This makes the picture operate the equivalent frequency of 50hz.
![](https://i.ytimg.com/vi/WA9Af82hF8Y/maxresdefault.jpg)