Slicer  4.8
Slicer is a multi-platform, free and open source software package for visualization and medical image computing

Widgets → Base Relation

File in Modules/Loadable/Measurements/WidgetsIncludes file in Base
qSlicerMeasurementsAngleWidget.hQTGUI / qSlicerWidget.h
qSlicerMeasurementsRulerWidget.hQTGUI / qSlicerWidget.h