HyperPhysics - Voltmeter
Wikipedia - Wheatstone bridge
Wikipedia - Wheatstone bridge
Straightforward article.
Wikipedia - Potentiometer - Theory of OperationLike the Wheatstone bridge, the Potentiometer is a favorite complex circuit for comprehensive exams.
HyperPhysics - GalvanometerTopic Resources
20 questions
concept review with practice items
figures for classroom presentation