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Method of testing work of a drill bit (10) of a given size and construction comprises the steps of drilling a hole with the drill bit (10) from a starting point Q) to an end point (T) and recording the distance between the starting point and the end point. Electric incremental real power signals (18) are generated, each corresponding to a force on the drill bit (10) over a respective increment of the distance between the starting point and the end point. Electric incremental signals (14) are also generated, each corresponding to the length of the increment for one of the respective incremental real power signals (18). The incremental real power signals and incremental distance signals are processed to produce a value corresponding to the total work done by the drill bit when drilling from the start point to the end point. When using such a work sample, a number of other events and / or conditions in a borehole may be tested.