  Second, even when we know something isn't functioning in the environment for which it was designed (by God or evolution or both, but more of that next), we can still trust judgments based on them, if we know a little something about the manner in which they are likely to be mistaken. So let's return to 14,200 feet on the West Buttress of Denali with our barometer last calibrated at sea level. Since we know something about the relationship between altitude and barometric pressure, we can extrapolate or estimate the true value from the reported value to derive a range in which the true value is likely to be (if we have precise data we can generate confidence intervals which under good circumstances would be quite narrow). And we can certainly trust certain comparative judgments: even if we are almost completely ignorant of how to correct for the altitude change, if the reading falls fast consistently for an hour, we can safely infer that a low pressure front is moving in.  So even a poorly calibrated instrument can be of use if we have appropriate understanding of its inner workings.