Removal of linear trend from a luciferase timecourse. (a) Reporter-enzyme activity emanating from a pair of tim-luc;cry+ antennae maintained in DD. The dashed line is a least squares regression line that was fit to these data. (b) The linear trend defined by this line was removed by subtracting the value on the line from the corresponding data point. Removal of this trend line results in the dashed line (in b). The luminescence fluctuations around this mean (which are necessarily altered in appearance by the detrending) indicates the remaining presence of nonlinear trends. After removal of these non-linear trends circadian rhythmicity is apparent (see text and Figures 5 and 6).