Pendulum is a weight suspended from a pivot so that it can swing freely.  When a pendulum is displaced sideways from its resting position, it iwill accelerate it back toward the equilibrium position. this force combined with the pendulum's mass causes it to swing back and forth Until its energy is expended.  It is an ancient tool.  Many were found in the great pyramids of Egypt.
It is believed the Egyptians, the Greeks and the Chinese also used pendulumts for divination. There is evidence the Oracle of Delphi answered questions using a pendulum.

 A dowsing pendulum is an small weight suspended on a cord or chain, used to obtain information which is not normally available. You could improvise a pendulum with an everyday object, such as a key chain, a nail or a ring on a string. However, a professional pendulum is best because it is weighted and balanced to be more sensitive and to swing more evenly.  This makes it more effective.

 

The pendulum, as an extension of the dowser, may be influenced both consciously and subconsciously by the thoughts, wishes or preconceptions of the dowser—making the responses inaccurate. The thoughts of the dowser, however slight, can be magnified effecting the response of the pendulum. Steps must be taken to prevent this.   There is nothing evil or unspiritual in using a pendulum. It is the thoughts of the dowser that determine the value of the use of the pendulum. It is wise to get the permission of someone you are going to dowse for.  Vague questions can result in senseless responses.

 

                                                                    

                                                                     This may be an ancient Egyptian pendulum