[Oberon] a module a page (keeps the mind sane)?

[Frans-Pieter Vonck]

I'm looking into the code that is written for the citizen science 
project Luftdaten.
The link below shows the code for firmware for a sensor node, the 
esp8266.
https://github.com/opendata-stuttgart/sensors-software/blob/master/airrohr-firmware/airrohr-firmware.ino

The firmware is written in the arduino language.
Arduino is not a modulair language, the main program is over 4000 lines 
of code.
+/- 75 pages (A4).

Does anyone remember where Niklaus mentions the ' one page of code, one 
module ' rule?

Greets,
F.P. Vonck