In the early 1950s transistors had not yet replaced vacuum tubes in most electronics. Tubes varied widely in their actual characteristics from tube to tube even of the same model. Engineers had developed techniques to ensure that the overall circuit was not overly sensitive to these changes so they could be replaced without causing trouble. The same techniques had not yet been developed for transistor-based systems, they were simply too new. While smaller circuits could be "hand tuned" to work, larger systems using many transistors were not well understood. At the same time transistors were still expensive; a tube cost about $0.75 while a similar transistor cost about $8. This limited the amount of experimentation most companies were able to perform.