I think it was an Amazing Architecture. As far as I know Complex Instruction Set CPUs (CISC) was slow and then outperformed by RISC one but Saturn was very smart:

- The basic Calculator arithmetic is handled by the CPU, the CPU precision is the SAME of the calculator, and the digits can be printed on screen with little effort.

- The tiny hardware stack make the CPU quick: you needn't to make a major memory access to POP or PUSH return address the stack.

- The original tiny data bus (4 or 8 bit) reduced the production costs for low-end calculator.

- I/O and power saving was tight integrated: for instance there was a "deep sleep" mode to save battery.

Also the HP15C has a very efficient poweer saving design: https://www.hpmuseum.org/forum/archive/index.php?thread-1776... (search for "SOS (Silicon on Sapphire)")

Italian article with English links: https://gioorgi.com/2020/arte-dimenticata-rpn/