# 1980s AVTEL 4 colour mechanical display, how is the pixel state reset?

I stumbled on a retro Dutch video from 1983 where a large four color mechanical display is shown. Each pixel consists of a cube which can be turned in order to change the pixel color between 4 colors (white, green, red and blue), a carriage moves behind the screen and slowly updates the screen by altering the rotation of the cubes. Ah this retro electro-mechanical stuff, I love it.

My question is: how does the update carriage know the rotational position for each of the pixels?

Or is the rotational state not obtained but reset in some way? The pixels have small cams on their sides, but they seem similar for each color, I can't really see it properly. When the carriage passes it performs only one color-shift per line (90 degrees), and each pixel is always cycled during an update, even for cases where there is no difference between the initial color and target color of the pixel.

Other details: The displays seems to be branded "AVTEL". And seems to consists of 3 smaller displays next to each other.

• how does the update carriage know the rotational position? cannot be answered by anyone that is not familiar with the device .... what are some of the ways that the update carriage would know the rotational position? can be answered – jsotola Mar 29 at 21:49
• @jsotola, obviously its 90 degrees. I've changed it. – BuysDB Mar 29 at 21:51