Chess programs can differ in depth of search or in the evaluation function applied to leaf nodes or both. Over the past 10 years, the notion that the principal way to strengthen a chess program is to improve its depth of search has held sway. Improving depth of search undoubtedly does improve a program's strength. However, projections of potential gain have time and again been found to overestimate the actual gain.
We examine the notion that it is possible to project the playing strength of chess programs by having different versions of the same program (differing only in depth of search) play each other. Our data indicates that once a depth of "tactical sufficiency" is reached, a knowledgeable program can beat a significantly less knowledgeable one almost all of the time when both are searching to the same depth. This suggests that once a certain knowledge gap has been opened up, it cannot be overcome by small increments in searching depth. The conclusion from this work is that extending the depth of search without increasing the present level of knowledge will not in any foreseeable time lead to .World Championship level chess. The approach of increasing knowledge has been taken in the HITECH chess machine.