Another fun, somewhat related poster from 1944: Chart of Electromagnetic Radiations [0], and a "color-corrected" version [1].
[0]: https://www.flickr.com/photos/llnl/9403051123
[1]: https://www.flickr.com/photos/acme-laboratories/31849902131
[0]: https://www.flickr.com/photos/llnl/9403051123
[1]: https://www.flickr.com/photos/acme-laboratories/31849902131
Not only it clips some colors for no reason (look at the blue background around "broadcasting radio" house -- the gradient transition is totally gone. I assume the editor just used lasso tool to select "white-ish" parts and replace them entirely with a single color, instead of using color level?), it didn't even correct the background to pure white (but some reddish color)? Ugh!
I scanned through it looking for any obvious errors or things we've changed our understanding of a lot since then.
There's one picture of using Radium radiation in hospital treatments that seems very old-fashioned.
That said, much does still hold true. Longwave is still used by giant shore installations to communicate with ships. (Mostly by coincidence. Long wavelengths can reach submerged submarines.) The aeronautic band is still used by aeronautic non-directional beacons. The AM broadcast band is still AM broadcast. Some of the amateur bands are still in the same place today.
The physics and electronics depicted seem accurate. Its creators were clearly informed of the cutting edge in the 1940s; it depicts a magnetron, which had been invented about a decade before, and not widely used until high-power models were developed and then applied to radar c. 1940. A section about the health effects of ionizing radiation is conspicuously absent to my modern eye.
"Variable speed of light" - https://en.wikipedia.org/wiki/Variable_speed_of_light