[makeworld]

What was the preferred way of doing FFT at that time?

[ants_everywhere]

hasn't the preferred way been Cooley-Tukey consistently since 1965?

https://en.wikipedia.org/wiki/Cooley%E2%80%93Tukey_FFT_algor...

[segfault99]

Bingo. We certainly learned about Cooley-Tukey in undergrad back then. That power station was 100% Hitachi Heavy Industries turnkey. The control rooms had Hitachi mainframe and some minicomputers running proprietary real time OS (I guess). These were the days when the video controller for a colour industrial process control raster display CRT was a waist-high cabinet. So you'd transduce the flicker and then transmit it via analogue current loop to a rack in the control room annex, convert back to voltage, A/D it... and crunch the FFT on one of the control room computers. Something like that. Cheap distributed compute just wasn't a thing at the time.