You can measure a long term trend, even if it's overwhelmed in the short term by much larger changes, by tracking local maxima/minima. Suppose that a circuit's

You can measure a long term trend, even if it's overwhelmed in the short term by much larger changes, by tracking local maxima/minima. Suppose that a circuit's voltage is either increasing or decreasing by 1V per hour, and your measurements ranging from 90V-110V. To determine the trend, you ignore the increase/decrease from one measurement to the next, and wait for it to hit 111 or 89.