Another improvement introduced in their core design involved the handling of the read wire. Reading a location in core works by powering the address in question, as if you wanted to write a "1" to that location. If the core was "already" holding a "1" nothing will happen. However, if the core was holding a "0", the power will cause the core to change polarity to a "1". The small amount of energy used to do this causes a pulse to be output on a different wire, the read line. So to read data, you write "1" to that location, if a pulse is seen on the read line the location originally held "0", and no pulse means it held "1".