It was a true PDE, not an ODE. The circuit was non-trivial, but though I knew PDEs at the time he told the story, I'd never used them on electronics (only heat

It was a true PDE, not an ODE. The circuit was non-trivial, but though I knew PDEs at the time he told the story, I'd never used them on electronics (only heat / pressure flow, and other physical engineering stuff) so I couldn't really understand what he was saying.