Berkshire has been below 1.3x book for 35% of the time over the last twenty years, and below 1.2x book for about 15% of the time. I personally am waiting for less than 1.3x book to make any additional purchases.

One question here is whether the buyback change in policy changes this math, especially given the growing pile of gold BRK is sitting on. I suspect it does.

Since the change in policy in mid-2018, BRK has been at 1.3 or below only 20% of the time and below 1.2 book less than 10% of the time. This may simply reflect an elevated market. But, and assuming to inflationary and deflationary factors affecting fair price to book ratio continue to roughly offset each other, I'd wager time below 1.3 will continue to be a shorter trip going forward, given BRK's ability and commitment to buying back shares at such prices. Not because BRK's a buyer affecting prices(though the effect of BRK moving to heavy buys on market sentiment shouldn't be discounted), but because it solves their biggest problem -- allocating their idle capital smartly and at scale.

It could just be a small sample and the final stages of a market bull run elevating prices. But I think the market rightly sees BRK as having big opportunities if its stock price swoons.