The first decision to be made was on the type of movement to be used. Without special treatment, battery-operated instruments are not appropriate for a spacewalk for safety reasons. Thus, quartz movements were not considered. The choice was therefore between mechanical and Spring Drive. The choice was decided by the need for safety and accuracy. As the watch will be exposed to a range of temperature from minus 20 degrees Celsius to plus 70, accuracy at extreme temperatures was the critical factor, and no mechanical watch can retain its accuracy in these conditions, because of the inherent instability in these conditions of the traditional escapement which regulates the time in all mechanical watches. Instead of a traditional regulator, Spring Drive has a Tri-synchro Regulator, an entirely new regulator that uses and generates mechanical, electrical and electromagnetic power! , and is less affected by temperature variations. Thus, Spring Drive was selected as the perfect mechanism for the task.