Whenever SpeedFan reads a new sample for any sensor, it stores it its current value and timestamp. Some sensors are read less often than others. For example: S.M.A.R.T. sensors are read every 60 seconds, whereas other temperatures are collected every 3 seconds. Whatever the sampling rate is, SpeedFan will always show the full available interval. The samples stored for each sensor will be limited. Currently this limit is set to 256 samples, but it might vary in the future. This means that SpeedFan will show, at most, the last 256 samples.

You can select which kind of sensors' readings to compare (temperatures, fan speeds, voltages) and, within each type, you can choose which sensors to graph at the same time. Each sensor will be automatically given a different color.