How the LOGO! program execution handles flags and outputs (M & Q).
How to do recursion in a LOGO!

0:00 - M & Q blocks and the program scan.
1:40 - A dozen AND gates in series!
2:08 - A dozen flags in series - a surprise!
3:30 - An M is just a Q with no terminal!
3:58 - A DIY one-shot.
5:04 - First scan pulse.
5:33 - Solving recursion limitation.

The Siemens LOGO! is a compact industrial PLC suitable for a huge variety of projects in industry, office and home automation.