Tangent skimming is a form of baseline constructed for peaks found on the upslope or downslope of a peak. The prerequisite is that the two peaks are not baseline-separated, and that there is a valley between them. Peaks detected by tangent skimming are referred to as rider peaks. If there is no valley, the peak is referred to as a shoulder.
The following figures illustrate the principle of tangent skimming:
Peaks without skimming, separated by valley and drop line
Tail Skimming