Originally a military specification.
We old RAF instrument bashers were led to believe it was standardisation for wartime production. Wartime mass-production meant using as many common parts as possible and instruments were no exception. For example, instrument cases and their glass faces from the same manufacturer often shared the same part numbers across instrument ranges - altimeters, airspeed indicators, VSIs and even RPM indicators might all share the same face plate and glass.
Aircraft of all types had what was called a "standard blind flying panel' installed. It wasn't just a standard layout either - you could even draw a complete blind flying panel from stock and just hook up the hoses. Take note of the way the same standard panel is integrated into both a
Lancaster pilot's panel and a
Stirling. You might find exactly the same panel integrated into the pilot's panel in
any other type of aircraft.