# How is the baseline determined for the various Data Pad integral calculations?

LabChart's Data Pad has four integral calculaton options available.  Each of these options uses a different method to determine the lower limit (or baseline) of the current selection's integral.  Below is a list of the various options with descriptions of how they each determines the lower limit for the integral.

Integral: Displays the integral of the selection, calculated as the sum of the data points, multiplied by the sample interval.  This method considers the horizaontal axis to be the lower limit of the selection's integral.

Integral relative to Minimum: Displays the integral of the selection, calculated as the sum of the data points minus the lowest value in the selection, multiplied by the sample interval.  This method considers a horizontal line that intersects the lowest value in the selection to be the the lower limit of the selection's integral.

Integral relative to Start: Displays the integral of the selection, calculated as the sum of the data points minus the first value in the selection, multiplied by the sample interval.  This method considers a a horizontal line that intersects the value at the start of the selection to be the the lower limit of the selection's integral.

Integral relative to Baseline: Displays the integral of the selection, calculated as the sum of the data points minus the value on a baseline (drawn from the value at the start (a) to the value at the end (b) of the selection), multiplied by the sample interval. This can be useful with a steadily drifting signal: in the example below, Integral above Baseline is an approximation of the shaded area. 