If the purchases are every year, they aren't going to be price sensitive.

Maybe he takes the "Added Principle" to the still-live but unlinked Berkshire Owner's Manual quite seriously:


AN ADDED PRINCIPLE

To the extent possible, we would like each Berkshire shareholder to record a gain or loss in market value during his period of ownership that is proportional to the gain or loss in per-share intrinsic value recorded by the company during that holding period. For this to come about, the relationship between the intrinsic value and the market price of a Berkshire share would need to remain constant, and by our preferences at 1-to-1. As that implies, we would rather see Berkshire's stock price at a fair level than a high level. Obviously, Charlie and I can't control Berkshire's price. But by our policies and communications, we can encourage informed, rational behavior by owners that, in turn, will tend to produce a stock price that is also rational. Our it's-as-bad-to-be- overvalued-as-to-be-undervalued approach may disappoint some shareholders. We believe, however, that it affords Berkshire the best prospect of attracting long-term investors who seek to profit from the progress of the company rather than from the investment mistakes of their partners.