distance and direction using these measurements in combination with the tool orientation measurements the driller can for example steer the drill bit 14 along a desired path 18 relative to the existing well 19 in formation 46 using any one of various suitable directional drilling systems including steering vanes a u201c bent sub u201d and a rotary steerable system for precision steering the steering vanes may be the most desirable steering mechanism the steering mechanism can be alternatively controlled downhole with a downhole controller programmed to follow the existing borehole 19 at a predetermined distance 48 and position e g directly above or below the existing borehole a telemetry sub 28 coupled to the downhole tools including ranging tool 26 can transmit telemetry data to the surface via mud pulse telemetry a transmitter in the telemetry sub 28 modulates a resistance to drilling fluid flow to generate pressure pulses that propagate along the fluid stream at the speed of sound to the surface one or more pressure transducers 30 32 convert the pressure signal into electrical signal s for a signal digitizer 34 note that other forms of telemetry exist and may be used to communicate signals from downhole to the digitizer such telemetry may employ acoustic telemetry electromagnetic telemetry or telemetry via wired drillpipe the digitizer 34 supplies a digital form of the telemetry signals via a communications link 36 to a computer 38 or some other form of a data processing device computer 38 operates in accordance with software which may be stored on information storage media 40 and user input via an input device 42 to process and.