Hint
When BRK.A takes a dip(as well as an up tick) ,so do all of the companies involved within that fund
So if you know what he owns you can get an overall idea about the trend in those companies and get in at a good entry level ,or out at a good exit point if you trade ...
In other words ,if you want to know how well the companies that are related to W.B are doing ,just check BRK.A . Then shop around