assembly 120 to transfer the weight to the drill bit 126 the weight provided by the drill collars 122 also assists the drill bit 126 in the penetration of the surface 104 and the subsurface formations 114 during drilling operations a mud pump 132 optionally pumps drilling fluid for example drilling mud from a mud pit 134 through a hose 136 into the drill pipe 118 down to the drill bit 126 the drilling fluid can flow out from the drill bit 126 and return back to the surface through an annular area 140 between the drill pipe 118 and the sides of the borehole 112 the drilling fluid may then be returned to the mud pit 134 for example via pipe 137 and the fluid is filtered the downhole tool 124 may include one to a number of different sensors 145 which monitor different downhole parameters and generate data that is stored within one or more different storage mediums within the downhole tool 124 the type of downhole tool 124 and the type of sensors 145 thereon may be dependent on the type of downhole parameters being measured such parameters may include the downhole temperature and pressure the various characteristics of the subsurface formations such as resistivity radiation density porosity etc the characteristics of the borehole e g size shape etc etc the downhole tool 124 further includes a power source 149.