He mentions the 90 cent dollar in this article...
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"If the market prices a departing partner’s interest at, say, 90¢ on the dollar, continuing shareholders reap an increase in per-share intrinsic value with every repurchase by the company."


He used to say shares should trade below 1.1x book, then he said it was 1.2x book, and most recently he has just said they need to be below intrinsic value, conservatively calculated. The above is just an example ("at, say, 90¢ on the dollar") of a situation where a repurchase would make sense; I think he could have also given an example of 99¢ on the dollar, and this would have still been consistent with the present criterion.

The 'conservatively calculated' is where the big question mark is: How does he do this calculation, and how conservative is it? I think the 'how' part is likely to be the 5 groves system that he has suggested we use. And I think it is clear from that system that there is already some built in conservativis. For instance, the fact that he gives no value to underwriting profits which have been very substantial over the years. But that's probably as far as we can go with what he has said to shareholders.