Program errors for the Ferranti Mark 1 computers were difficult to find. Programmers would sit at the computer control desk and watch the computer perform one instruction at a time in order to see where unintended events occurred. However, computer time became more and more valuable, so Dr Bennett suggested that Woods write a diagnostic program to print out the contents of the accumulator and particular store lines at specific points in the program so that error diagnosis could take place away from the computer. The challenge of her routine, 'Stopandprint', was that it had to monitor the program under diagnosis without interfering with it, and the limited space in the fast store made this difficult. Along with Bennet and Dr D.G. Prinz, Woods was involved in writing interpretive subroutines that were used by the Ferranti group.