History of Tuning Indicators: meters, graphs, Magic Eye, LED
I was doing some research into old meters and found the pic of this amazing radio the 7-Tube-Piano-Type". It featured Separate Voltmeters and Milliamp-meters on a Ducretet radio. The article it is mentioned in is very good and titled simply History of Tuning Indicators: meters, graphs, Magic Eye, LED.
More about this radio here.
The Radio Museum is a great resource if you haven't stumbled upon it check it out here http://www.radiomuseum.org .