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By Ken Haapala, President,The Science and Environmental Policy Project

**False Precision:** In their early education, many students of science faced the problem of significant numbers (digits). A useful rule of thumb was that the chain was only as strong as its weakest link. In measurement, the less precise instrument making the measurements determines precision of any dataset representing the measurements. A mathematical operation does not add precision to the instruments, or the dataset. For example, as discussed in the January 21 TWTW, the widely used Automatic Surface Observing System (ASOS) instruments at airports have a precision of plus or minus 1 degree C (1.8 F, correctly, 2 F). Surface datasets using these measurements cannot be more precise than these instruments. Yet, routinely, some government agencies report data, after mathematical manipulation, with far greater precision – to one-hundredths of a degree C. Such precision is false.

Writing in the non-conservative *Boston Globe*, columnist Jeff Jacoby gives a simple illustration on how small errors in measurement can compound in a computer model with many small errors. Any assumption that the errors will cancel each other out needs to be demonstrated. However, in the reports of the UN Intergovernmental Panel on Climate Change (IPCC) and its followers, such cancellation of errors is not demonstrated.