My colleague Thomas Docherty is wrong ("Total disclosure a sign of the academy's time-and-motion sickness", 30 July).

The Transparent Approach to Costing (Trac) is not a time-and-motion study. Time-and-motion used surveillance to measure workers' time against effort. Trac measures only time - and there is no surveillance.

Time-and-motion observers aimed to compress workers' efforts to minimise the time spent on particular tasks. Trac aims to cost time, but academics, reporting anonymously, are free to decide how to use it, how much time to use and how to report its uses.

Trac raises issues of subjectivity and ambiguity. The numbers it generates are, like all statistics, social artefacts that capture reality imperfectly. Docherty makes much of Trac's reduction of the hours reported by each person to percentages of the working week: but as he surely knows, this is a device to foil those who make a virtue of working excessively long hours - as he does.

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Universities that operate Trac effectively gain an understanding of which activities result in financial surpluses or losses. Docherty and I agree that money is not everything: most of the academy's goods should not be measured in cash-flow terms, and something that does not pay for itself may still be worth doing. But an activity that makes a loss requires others to pay for it - private donors, fee-payers, taxpayers or other academic activities that turn a profit. Without Trac, such payments would remain concealed.

Underfunding is our real enemy. Trac is just one of our spies.

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Mark Harrison, Department of economics, University of Warwick.