What critical event in 1936 signaled the official end of the mechanical era for UK broadcasting standards?

Answer

The BBC’s decision to launch its regular high-definition service

The BBC adopted the electronic system as the standard when it launched its regular high-definition service in 1936, leading to the transition away from Baird's mechanical Televisor technology.

What critical event in 1936 signaled the official end of the mechanical era for UK broadcasting standards?
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