in step 671 as will be explained in more detail in connection with fig3 fig3 illustrates the modify byte operation in step 648 the test equipment waits in step 701 for the input of a key then it is checked in step 702 as to whether the key is hexadecimal key a hexadecimal key is either a number between 0 and 9 or a character between a and f if a hexadecimal key is input its value is saved as al for later use in step 704 if a non hexadecimal key is input the flow proceeds to step 703 where it is determined as to whether return is input if that is the case the flow proceeds to the end in steps 718 if it is determined in step 703 that a key different from the return keys input the test equipment waits in step 701 for the input of another key steps 705 to 708 709 to 712 and 713 to 716 are similar to steps 701 to 704 however the key input in step 705 is saved as a 2 for later use the key input in step 709 is saved as v 1 for later use in step 712 and the key input in step 713 is saved for later use.