The ISA article dated August 1, 2003 entitled "Top technologies and Events" has a short paragraph on an innovation for pneumatics.
Pneumatic Instrumentation
In 1928, Foxboro's first pneumatic operational amplifier laid the groundwork for an entire generation of pneumatic instrumentation, much of it still recording industrial processes in plants around the world.  A year later, Foxboro followed with the first proportional -
plus-reset (integral) controller.
Since a valve positioner is a proportional controller, the signal to it being its setpoint, the  ball valve position being the process variable, and its purpose to zero the error between the setpoint and the valve position, I suspect Foxboro's innovation was critical to a successful proportional positioner.
And if Foxboro invented (and presumably patented) the pneumatic op amp, it's likely they'd have been in the market early on.
This reminds me of Dornberger's book, 'V2.' He had a chapter that described the important engineering developments in that project under trying circumstances.
One was the introduction of acceleration feedback in the directional control. Their controller calculated the second derivative of displacement.
It's a book worth reading and re-reading. I lost count of the number of times.

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