I think I did this right, does your log-log look something like below?
Morningstar gave me the data until 1996, I’m not sure if I can get anything further back.
Assuming I did the log-log the way you described then the linear regression is giving a BRK.B stock price of ~$281 with a BRK.B book value of $209.5; @DetroitBadBoy , that doesn’t seem like the back-up-the-truck level. But this is a different analysis period and kind of like comparing apples to oranges.
This is an incredibly simple approach and it seems informative. I love it. Thanks for sharing @rrr12345!