as previously explained the identification information can uniquely identify each casing collar 64 with an alpha numerical numerical or other designator in addition using previously prepared well logs the depth of each uniquely identified casing collar 64 can be ascertained as also shown in fig4 a the reader device 70 includes the transmitter 73 for transmitting transmission signals to the identification devices 72 and the receiver 71 for receiving the response signals from the identification devices 72 the reader device 70 can be powered by a suitable power source such as a battery or a power supply at the surface in addition the reader device 70 includes a memory device 112 such as one or more integrated circuit chips configured to receive and store programming information the reader device 70 also includes a telemetry circuit 114 configured to transmit control signals in digital or other form through software 116 to a controller 118 or alternately to a computer 122 as is apparent the software 116 can be included in the controller 118 or in the computer 122 in addition the computer 122 can comprise a portable device such as a lap top which can be pre programmed and transported to the well site also as will be further explained the computer 122 can include a visual display for displaying information received from the reader device 70 the controller 118 or the computer 122 interface with tool control circuitry 120 which is configured to control the perforating tool 68 as required in the illustrative embodiment the tool control circuitry 120 is in signal communication with the detonator 74 fig3 c of the perforating tool 68 the tool.